Short answer: no. Long answer: it depends on definitions but on most sensible definitions still no.
I'm summarising the excellent analysis by UK fact checkers Full Fact as presented here. This analysis primarily relates to the UK (where the debate about EU influence is probably more contentious than anywhere else) but the key issues apply in other countries as well.
The core problem in getting to any meaningful answer is how and what counts as a law. If we just count acts of parliament then major bills (like the 500 page Health and Social Care act which completely reformed the NHS) count equally with the three page act clarifying the rules on VAT fraud.
But acts of parliament are not the only things that count as law:
The figures depend on which UK law is included in the calculation, and the extent of ‘EU influence’ that we look at. There is no single interpretation of UK law, it can include: Acts put in place by the UK Parliament; rules and regulations drawn up by Ministers; and regulations produced by the EU which apply here in the UK.
Because of this:
The House of Commons Library warned that “there is no totally accurate, rational or useful way of calculating the percentage of national laws based on or influenced by the EU.”
Full Fact used the House of Commons Library analysis to produce three estimates in decreasing order of significance and impact:
1: Acts put in place by UK Parliament with EU influence – accounts for 10-14%
2: Regulations influenced by or related to the EU – accounts for 9-14%
3: EU regulations and regulations influenced by or related to the EU – accounts for 53%
But they also warn that the broader the definition, the less relevant to any estimate of real EU influence is (my emphasis):
Aside from problems of definition, these calculations are based on a search of national law databases and the EU’s EUR-Lex database and therefore have immediate problems in terms of how robust the search terms were and whether all ‘laws’ were inputted to the database. Incorporating or excluding EU regulations – some of which relate to things such as olive growing regulations and therefore will not directly impact on the UK – are likely to either overestimate EU influence or underestimate it. Counting these things alone does not tell us enough about where the power lies.
So, even on the most relaxed definition, the numbers are far short of claims from EU critics that >75% of our laws are written in Brussels.
On a stricter, more natural interpretation the ratio could be <15%.
It is also worth noting that similar problems apply to calculations in other (less EU skeptical) countries:
There has also been a figure of 85% floated, which seems to originate back to a calculation made in relation to Germany, based on figures provided in the German parliament in 2005. Aside from issues with the calculation itself (which has similar problems to the ones we discuss here), Germany is a federal country whose individual states have significant law-making powers that are not taken account of in calculating the 85%. This makes it very hard to relate the figure to the UK.