Backbencher Jacob Rees-Mogg, who took over the chairmanship of the Brexit-supporting European Reform Group of Tory parliamentarians earlier this week, urged the Prime Minister to stand up to Remainers in the upper house over her flagship EU Withdrawal Bill.
Labour and Lib Dem peers are expected to attempt to drastically alter the legislation when it goes to the Lords for scrutiny at the end of this month.
Mrs May is expected to appoint 10 more Tory peers soon to help steer the Bill through the chamber, where the overwhelming majority of members voted for Britain to stay in the EU in the 2016 referendum.
Mr Rees-Mogg urged her to go much further in strengthening the Brexit-supporting side of the Lords however.
He said: “She should keep up her sleeve the ability to appoint enough peers to get business through.
“If the House won’t play by the constitutional rule book, then the Prime minister has to use the extra measures available to her.”
Mrs May could ennoble “a couple of hundred” Brexit-backing Tories, the MP said.
Mr Rees-Mogg said: “There is no point in going off half cock.
“They are not there to challenge the democratic will.”
Peers are due to begin scrutinising the EU Withdrawal Bill on January 30, with several weeks of debate to follow.
Remain-backing peers are expected to table dozens of amendments designed to water down Britain’s break from Brussels by keeping the country in the European single market and EU customs union.
They are understood to believe that the Prime Minister’s failure to win a Tory majority in last year’s general election frees them from having to obey the so-called Salisbury Convention that obliges peers to respect manifesto commitments of the ruling party.
Ministers are braced for a major constitutional showdown that could lead to the legislation being passed back and forth between the Commons and the Lords.
Earlier this week, Government sources indicated that Mrs May will snub George Osborne, who led the Treasury scare campaign against Brexit, by refusing to offer him a peerage.
He is expected to become the first former chancellor in decades not to be offered a peerage.