The British Prime Minister Theresa May has told Tory rebels that if they defy her over Brexit legislation, it will undermine the UK's position in negotiations with Brussels.
Mrs May urged backbenchers not to support Lords amendments to the EU (Withdrawal) Bill when it returns to the Commons on Tuesday because a government defeat would send the wrong signal.
Addressing a meeting of the backbench 1922 committee on Monday ahead of a series of crunch votes, the Prime Minister said: "We must think about the message Parliament will send to the European Union this week.
"I am trying to negotiate the best deal for Britain. I am confident I can get a deal that allows us to strike our own trade deals while having a border with the EU which is as frictionless as possible.
"But if the Lords amendments are allowed to stand, that negotiating position will be undermined."
Mrs May’s government is thought to be most vulnerable on two amendments - one on the customs union and the other giving Parliament a decisive say over what happens next if it rejects a final Brexit deal.
Meanwhile, Taoiseach Leo Varadkar has raised the possibility of delaying Brexit to allow more time to negotiate the UK's exit deal.
He said extending the 29 March departure date is one of a number of "different scenarios" that could be pursed if a withdrawal agreement fails to materialise in the coming months.
In an interview broadcast on TV3, Mr Varadkar also raised the prospect of scheduling an extra EU Council summit this year if sufficient progress is not made by October's crunch meeting.
The autumn summit is seen by many as an effective deadline for a withdrawal treaty to be sealed ahead of ratification by member states.
The EU and UK remain at odds over the shape of a "backstop" position to maintain free movement at the Irish border, if a wider trade deal is not ultimately agreed, with Prime Minister Theresa May struggling to secure consensus within her own Cabinet.
Mr Varadkar said while the Government was making contingency plans for a hard Brexit, he insisted that preparatory work did not include for the provision of infrastructure on the border with Northern Ireland.
When the UK formally notified the EU in March 2017 of its intention to leave the union - by triggering Article 50 of the Lisbon treaty - a two-year deadline for its exit was automatically set.
Stressing that a no-deal scenario is still hypothetical, Mr Varadkar added: "You'll know that there are a number of different scenarios that could arise if we're in a no-deal situation.
"For example, it is possible to extend Article 50, to allow more time for negotiations to take place. There is the possibility of an interim deal, or a transition period, pending an outcome or final negotiations around the transition period.
"But one of our red lines - and this should be no surprise to anyone - is that we cannot countenance a hard border with physical infrastructure, with customs and checks - all of those things - between Northern Ireland and Ireland.
"That would be an abrogation of the Good Friday Agreement, a solemn agreement we made 20 years ago, and a legal agreement that is registered with the United Nations, signed by the United Kingdom Government," he said.