A senior Tory MP has said he would begin to question the existence of the House of Lords if peers start "messing around" with the Brexit bill.
Peers are discussing legislation which will give the prime minister the power to invoke Article 50 and begin the process of Britain leaving the EU.
Monmouth MP David Davies said peers had to "realise the people have spoken".
Former Neath MP Lord Peter Hain said peers could and would win "important amendments" to the bill.
"We have voted to leave the EU and the Lords need to come on board and realise that the people have spoken," he added.
Former Labour Welsh Secretary Lord Hain said the House of Commons would "triumph over the Lords, but we will win some important amendments including an open border in Northern Ireland".
The Lords continue their scrutiny of the Brexit bill next week.
Mr Davies said: "The Lords can play a useful role in revising difficult and complicated legislation, but this is very simple, we're giving the prime minister the power to pull out of the European Union.
"If they want to start messing around with that, I think it's not just the far left that questions their existence, it's going to be people like me as well, so they better start thinking about that.
"I am a true blue Conservative and I have never really questioned the Lords, but I am starting to think to myself as I look around the rest of the United Kingdom 'there's no second chamber in Wales and there's no second chamber in Scotland'."
Lord Hain added: "It's first time in the history of Parliament that a Tory government has not had an automatic majority because Tony Blair abolished 600 hereditary peers.
"They're in the same position now that all Labour governments have always been in."
- The Wales Report is on BBC One Wales at 22:40 on 22 February