LONDON - Britain's House of Lords could delay a bill empowering Prime Minister Theresa May to trigger Brexit, with EU citizens campaigning for their rights to be protected as debate gets under way Monday.

The upper house of parliament was to start considering the draft legislation after it was overwhelmingly approved by the elected lower House of Commons earlier this month. But the bill's passage through the Lords may not be smooth as May's Conservative Party does not hold a majority in the unelected chamber, which may try to push through amendments to the law. Peers are proposing changes, including measures to guarantee the rights of EU nationals in Britain, and defining how parliament votes on a final Brexit deal. May urged the Lords to follow the lead of the Commons and neither amend the bill nor delay it, although the government is still expecting to stick to its timetable of triggering Brexit by the end of March.

"There will be debate and scrutiny in the House of Lords, but I don't want to see anybody holding up what the British people want... which is for us to deliver Brexit, to leave the European Union," she said.

The bill gives May the right to trigger Article 50 of the European Union's Lisbon Treaty, the formal procedure to start negotiations on leaving the bloc.

The government presented the short bill after losing a high-profile court battle in which judges ruled that May must have the consent of parliament before beginning divorce proceedings with Brussels.

The legislation sailed through the Commons earlier this month by 494 votes to 122.

In a June referendum, 52 percent of voters opted to leave the EU after four decades of membership, sending shockwaves across Europe.

But the government could face greater challenges in the Lords, where only 252 of the more than 800 members are from the centre-right Conservatives.

Peter Mandelson, a lord from the main opposition Labour Party and former European trade commissioner, said there was a "strong body of opinion" on the seriousness of the two proposed changes.

The Lords will debate the bill on Monday and Tuesday, before two further days of discussions next week and a final reading scheduled for March 7.