LONDON (AP) — The British government began battle Thursday to pass a major plank of its Brexit plans through Parliament, amid faltering progress in divorce talks with the EU.

Lawmakers are starting debate on the European Union (Withdrawal) Bill, which will revoke thousands of EU laws and regulations and replace them with domestic statute on the day the U.K. leaves the bloc.

The government says the legislation is crucial to disentangle Britain from the EU after more than four decades of membership.

Prime Minister Theresa May said it would "prevent a cliff-edge for people and businesses, because it provides legal certainty."

Critics say the bill gives the government powers to change laws without parliamentary scrutiny.

The main opposition Labour Party calls the bill "a power grab" and says it will vote against it when it is put to lawmakers next week.

Britain is due to leave the EU in March 2019, two years after it triggered the official exit process.

Exit negotiations have made little headway, with the EU and Britain accusing one another of failing to compromise. U.K. Brexit Secretary David Davis has urged EU negotiators to show "flexibility" and begin negotiating a future economic relationship that would include a free trade deal between Britain and the bloc.

The EU says that can't happen until substantial progress has been made on divorce terms, including the amount Britain must pay to settle its financial commitments to the Brussels-based bloc.

Britain wants to move on to the second stage of talks in October. But Herman van Rompuy, a former European Council president, said Thursday that the chances of that happening are "in the neighborhood of zero."