He was terminated as a source from the FBI for talking with the media, and the FBI was precluded from using him by internal protocols
Congressional investigators know that Christopher Steele, the former British spy who compiled the Trump dossier on behalf of the Clinton campaign, kept supplying allegations to the FBI after the 2016 election — and even after he was terminated as a source by the bureau for giving confidential information to the media.
Because he had broken his agreement with the FBI, bureau procedure did not allow agents to keep using Steele as a source.
The Hill reports
The FBI specifically instructed Steele that he could no longer “operate to obtain any intelligence whatsoever on behalf of the FBI,” those memos show.
The firing took place Nov 1, 2016.
That's pretty clear that the FBI "officially" barred him; however, Bruce Ohr Associate Deputy Attorney General with deep ties to the FBI and whose wife worked at Fusion GPS, the firm that hired Steele, operated a back channel to keep getting Steele's "information".
[The FBI continued to use Steele as a source] by devising a system in which Steele spoke regularly with Bruce Ohr, a top Obama Justice Department official whose wife worked for Fusion GPS, which hired Steele to search for dirt on Donald Trump in Russia. Ohr then passed on Steele's information to the FBI.
In a highly unusual arrangement, Ohr, who was the fourth-highest ranking official in the Justice Department, acted as an intermediary for a terminated source for the FBI's Trump-Russia probe. His task was to deliver to the FBI what Steele told him, which effectively meant the bureau kept Steele as a source
The source of much above appear to be the Nunes memo. From the Atlantic, citing this memo
Before and after Steele was terminated as a source, he maintained contact with DOJ via then-Associate Deputy Attorney General Bruce Ohr, a senior DOJ official who worked closely with Deputy Attorneys General Yates and later Rosenstein.
Shortly after the election, the FBI began interviewing Ohr, documenting his communications with Steele. For example, in September 2016, Steele admitted to Ohr his feelings against then-candidate Trump when Steele said he “was desperate that Donald Trump not get elected and was passionate about him not being president.” This clear evidence of Steele’s bias was recorded by Ohr at the time and subsequently in official FBI files—but not reflected in any of the Page FISA applications.
So while the FBI was precluded from interacting with Steele as a source officially, they were clandestinely in contact with him 12 additional times for information after his firing.
The 12 meetings were documented in what are called 302 reports, in which FBI agents are required to document meetings. The 302 reports came to light from Senate testimony and came public when the Chairman, Sen Grasserly, requested that they be declassified.
The dates of those official meetings are: The first was Nov. 22, 2016. After that, the FBI interviewed Ohr on Dec. 5; Dec. 12; Dec. 20; Jan. 23, 2017; Jan. 25; Jan. 27; Feb. 6; Feb. 14; May 8; May 12; and May 15. Remember that the firing took place Nov 1, 2016.
On 08/07/18, hundreds of new emails and memos have been disclosed. See the Hill link above. They back the Senate Judiciary findings that Ohr was encouraging Steele to keep operating.
Yet, Steele asked Ohr in the Jan. 31 text exchange if he could continue to help feed information to the FBI: “Just want to check you are OK, still in the situ and able to help locally as discussed, along with your Bureau colleagues.”
“I’m still here and able to help as discussed,” Ohr texted back. “I’ll let you know if that changes.”
Steele replied, “If you end up out though, I really need another (bureau?) contact point/number who is briefed. We can’t allow our guy to be forced to go back home. It would be disastrous.”