Updated

Britain's top official for leaving the European Union told lawmakers on Monday they should pass an EU exit bill "without further delay" so the government can start formal divorce talks with the bloc.

Brexit Secretary David Davis urged Parliament to approve a bill authorizing exit talks without amendments, "so the prime minister can get to work on the negotiations."

Prime Minister Theresa May says she will invoke Article 50 of the EU's key treaty, the trigger for two years of exit negotiations, by March 31.

But she can't do it until Parliament approves. The House of Commons and House of Lords are battling over the bill's contents, with the Lords wanting it to include a promise that Parliament will get to vote on the final deal between Britain and the 27-nation bloc.

Members of the Lords have also called for explicit protection for the rights of EU citizens living in the U.K. after Brexit.

Davis said the government had a "moral responsibility" to the 3 million EU citizens living in Britain and the 1 million Britons in other member states, and intends to guarantee their rights as soon as possible after exit talks start.

"That is why we must pass this straightforward bill without further delay so the prime minister can get to work on the negotiations and we can secure a quick deal that secures the status of both European Union citizens in the U.K. and also U.K. nationals living in the EU," he said.

The House of Commons, where the governing Conservatives are in a majority, will vote later Monday on whether to remove the Lords' amendments

If the unelected House of Lords digs in its heels and tries to restore them, the parliamentary feud could delay the bill for several days — but ultimately, the elected Commons will prevail.

If the Lords concede late Monday evening, the bill will become law once it receives the formality of royal assent. May will then be in a position to trigger Article 50.

Amid speculation she could do that as early as Tuesday, May spokesman James Slack repeated the government's position that it would trigger Article 50 by the end of March.

"I've said 'end' many times but it would seem I didn't put it in capital letters strongly enough," he said.

Pro-EU lawmakers accuse the government of running roughshod over the concerns of the 48 percent of Britons who voted to stay in the EU by rejecting the Lords amendments.

The government says voters have spoken and Britons must now unite behind the decision to leave. But May's government got a shock rebuff Monday from Scottish First Minister Nicola Sturgeon, who announced she would seek authority to hold an independence referendum in the next two years because Britain is dragging Scotland out of the EU against its will.

While Britons overall voted to leave the EU, Scottish voters backed remaining by 62 to 38 percent.

Sturgeon said she would seek to hold a referendum between the fall of 2018 and the spring of 2019 so that Scotland won't be "taken down a path that we do not want to go down without a choice."

In a 2014 referendum, Scottish voters rejected independence by a margin of 55 percent to 45 percent. But Sturgeon said that the U.K.'s decision to leave the EU had brought about a "material change of circumstances."