TLDR: if we frame the claim narrowly about migrant inflows, it's false as Fidesz has portrayed it; if we consider the context of all the other stuff Fidesz has blamed on Soros, then it looks like a piece of a much bigger puzzle: a Fidesz strategy combining anti-Muslim with (veiled?) anti-Semitic rhetoric, essentially they are alleging a Jewish[-led] plot to flood Europe with Muslims, killing two birds with one stone, from Fidesz's viewpoint.
The article you link says:
Fidesz leaders claim Mr Soros wants Europe to accept one million immigrants annually for labour, according to the Financial Times.
A spokesman for Mr Soros, Michael Vachon in July dismissed the idea that the financier and philanthropist was promoting a scheme to import millions of illegal immigrants into Europe.
He said: “Soros's actual position on migration is that the international community should provide more support to the developing countries that today host 89 percent of refugees and that Europe should accept several hundred thousand fully screened refugees through an orderly process of vetting and resettlement.”
Last year, Mr Soros wrote a column on a website that stated that the EU could reduce illegal migration by accepting 300,000 refugees annually.
The last statement appears to be correct:
The refugee crisis is not a one-off event; it augurs a period of higher migration pressures for the foreseeable future, due to a variety of causes including demographic and economic imbalances between Europe and Africa, unending conflicts in the broader region, and climate change. Beggar-thy-neighbor migration policies, such as building border fences, will not only further fragment the union; they also seriously damage European economies and subvert global human rights standards.
What would a comprehensive approach look like? It would establish a guaranteed target of at least 300,000 refugees each year who would be securely resettled directly to Europe from the Middle East — a total that hopefully would be matched by countries elsewhere in the world. That target should be large enough to persuade genuine asylum-seekers not to risk their lives by crossing the Mediterranean Sea, especially if reaching Europe by irregular means would disqualify them from being considered genuine asylum-seekers.
This could serve as the basis for Europe to provide sufficient funds for major refugee-hosting countries outside Europe and establish processing centers in those countries; create a potent EU border and coast guard; set common standards for processing and integrating asylum-seekers (and for returning those who do not qualify); and renegotiate the Dublin III Regulation in order to more fairly share the asylum burden across the EU.
[...] Canada provides a good role model (although its geographic context differs from Europe’s). In just four months, it admitted 25,000 Syrian refugees and is integrating them through public-private partnerships and local nonprofits. The government has promised to accept another 10,000 Syrians by year’s end and 44,000 refugees in total in 2016. (At the same time, it is admitting 300,000 migrants in total every year; this would be the equivalent of the EU accepting 4.5 million migrants annually.)
So the number he actually called for is lower (300,000), and Soros is talking about asylum-seekers. I suspect that, as a general rule, in the discourse of Fidesz leaders there's probably no distinction made between asylum-seekers and immigrants "for labour". On the other hand, Soros does mention that hypothethical 4.5 million migrants if EU were like Canada, but he stops short of actually calling for that (migration) to happen. But Soros' article does goes on to say:
given its aging population, Europe must eventually create an environment in which economic migration is welcome. Merkel opened Germany’s doors wide to refugees, but her generous act was not well thought through; it ignored the pull factor. A sudden influx of more than a million asylum-seekers overwhelmed the capacity of the authorities, turning public opinion against migrants. Now the EU urgently needs to limit the overall inflow of newcomers, and it can do so only by discriminating against economic migrants. Hopefully, this is temporary, but while it lasts, it is both inappropriate and damaging.
So Soros does favor some non-zero level of economic migration into the EU, but the rest of his article doesn't propose a specific figure for that.
And an article published by The Telegraph about a month after the on in Express details another rebuttal:
It pays particular attention to the million migrant claim. Although it concedes Mr Soros did say in 2015 that because of the war in Syria the EU would have to accept “at least a million asylum seekers” a year, it points out that a year later the financier reduced his estimate to just 300,000.
Also of note, both newspaper articles also talk about Orban's claim that Soros was behind the resettlement plan of asylum-seekers already in the EU (which sounds a lot more like a conspiracy theory); you don't seem to be asking about that issue, but only about inflows, so I limited my answer to that.
I hesitate to add much more than this as not steal Tim's thunder, but some comments on the affair from a columnist in the Guardian, rearranged slightly:
In Budapest, the far right has Jews plotting to destroy Christian Europe by bringing in Muslims.
The [Fidesz-governed] state has saturated the country with propaganda portraying the liberal Hungarian-Jewish financier George Soros as a menace to the nation. The rootless cosmopolitan is planning “to resettle at least one million immigrants annually” in the EU in general and Hungary in particular, Fidesz warns. As Soros does not command a government, Fidesz would have struggled to explain how he could flood Europe with Muslims. It’s as if UK ministers were pretending the choice before the electorate was between the Conservative party and Human Rights Watch.
But Orbán rarely has to explain. Most TV stations and newspapers obey the government and their hack propagandists have worked to turn the marginal NGOs Soros funds, with no power beyond the ability to seek judicial review of the treatment of refugees, into agents of a supernaturally powerful Jew.
And for the wider context in which Fidesz makes these claims, a 2016 snapshot:
Soros became a prominent scapegoat through Viktor Orbán’s mysterious references to “háttérhatalom/háttérhatalmak,” which I translated as “clandestine power/s.” As far as I can figure out, this clandestine power consists of the U.S. government, the Clintons, George Soros, and the civic organizations financed by him. According to government propaganda, Soros is supporting Hillary Clinton financially for the sole purpose of electing someone president of the United States who has an unfavorable view of the Orbán government. This propaganda, interestingly, seems to have fallen mostly on deaf ears. Only 19% of the people think that Soros and unnamed “clandestine powers” influence Hungarian politics, and a whopping 65% think that “this is just a communication strategy to direct attention away from other serious domestic problems.”
Soros’s name came up on two more occasions. The answers to these questions show that about 30% of Hungarians believe that “George Soros personally has something to do with the refugee crisis” as opposed to 41% who believe otherwise. Note that a lot of people couldn’t or didn’t want to answer. The same was true about Soros’s attitude toward the Hungarian government. To the question whether “he intends to overthrow the Hungarian government” 29% answered in the affirmative. These are high numbers, especially since only 40% think that these accusations are bonkers.
General questions about the refugee crisis show the depth of Hungarians’ confusion over the issue. Seventy-one percent of the respondents believe that “the goal of the refugee crisis is the weakening of Europe.” It is equally worrisome that 53% of the people believe that “American interest groups intentionally generated the refugee crisis.” It is also discouraging that 62% think that “a small elite controls the whole world.” Finally, on another level, 25% of the population believe in the deliberate spraying of people with poisonous materials (chemtrails).
As to the impact of Fidesz's latest claims against Soros there's a 2018 survey:
59 percent of respondents do not believe that NGOs are setting up “immigration organizing offices” to execute the “Soros-plan”, according to a recent poll conducted by Policy Agenda at the request of news site zoom.hu.
Even though the Hungarian government has spent tens of millions of dollars demonizing George Soros and civil society, only 27 percent of the Hungarian society agree with the statement “there are civil organizations in Hungary that seek to open immigration offices to help implement the Soros-plan.”
It comes as no surprise that voters of the ruling Fidesz party are the most receptive to the conspiracy theories of the government propaganda, with 39 percent of them believing that NGOs are seeking to open immigration offices to settle scores of Muslim immigrants in Hungary as per the “Soros-plan”.
What is remarkable, however, is that even the majority of Fidesz voters, some 52 percent, do not agree with the statement. The vast majority of left-wing-liberal voters (78 percent) reject the statement, but even among them, 16 percent believe the government propaganda. 66 percent of Jobbik voters reject the statement, while 24 percent agree with it. Undecided voters also reject the statement by a ratio of nearly three to one.
I think I'm digressing to much here already... since you didn't ask if Hungarians actually buy these claims.
And as if those conspiracy claims coming directly Fidesz weren't enough... a couple of monthts later they've endorsed some more explicit ones:
The book, titled “George Soros,” was originally written in 2016 by Andreas von Rétyi and questions, among other things, whether “Soros caused the refugee crisis.” Von Rétyi’s other books include one about “UFO secrets,” as well as another that backs a so-called 9/11 truther conspiracy theory that the U.S. government was involved in the September 11, 2001 terror attacks.
Originally in German, the Soros book will be printed in Hungarian by a publisher close to Prime Minister Viktor Orbán’s government, according to Spiegel. The plan is for 5,000 copies to be printed and distributed to politicians as well as activists across the country.
“The book is a detailed and accurate piece,” János Halász, a Fidesz spokesman, told broadcaster RTL Klub, according to Spiegel.