U.K. Prime Minister Theresa May is preparing to trigger Brexit but must first pacify rebels within her own governing party.

With a vote set for Monday on a bill granting May the authority to open divorce talks with the European Union, some Conservative lawmakers are pushing for Parliament to have a say on what happens if negotiations break down without an agreement. If May refuses to bow to their demand, they may oppose her in the vote, according to lawmaker Alistair Burt, a former minister.

The lower house of Parliament is being asked by May to delete conditions imposed by the unelected upper House of Lords to her draft law, so she can press ahead and start Brexit by March 31. Peers amended the bill to protect residency rights of EU nationals living in the U.K. and guarantee legislators a binding vote on the outcome of talks with the EU, even if there is no pact.

“Parliament must be involved and I want the government to give an assurance about Parliament’s role if there is no deal,” Burt said in a telephone interview on Friday. “If they can’t, it may not be possible to get in the way of the Lords’ amendment.”

Among other senior Tories pressing May over Parliament’s role shaping Brexit is former cabinet minister Nicky Morgan. She said by phone she hadn’t decided whether to oppose May and keep the Lords’ amendment and was “waiting to hear how the government deals with how Parliament has a say if no deal is agreed.”

Quick Response

The prime minister is taking on her domestic opponents as her counterparts in the other EU nations brace to engage. At a summit in Brussels on Friday, European Council President Donald Tusk said they would respond within 48 hours of May invoking Article 50 of the Lisbon Treaty, which formally begins the exit process.

May also got a reminder of just how tough those talks will be. EU governments said they will stand as one to preserve the stability of the bloc and that May will not to be allowed to “cherry pick” the best bits of EU membership. They are also threatening to impose an exit fee on the U.K.

May says she’d be willing to walk away from Brexit talks because “no deal for Britain is better than a bad deal.” Her critics who support the conditions imposed on the bill by the Lords’ say legislators must have the power to stop her quitting negotiations without an agreement.

While a smooth process in Parliament could in theory let May notify Brussels of her intention as soon as Tuesday, she could still delay. Her room for maneuver is potentially limited by Dutch elections on March 15, a conference of the Scottish National Party March 17-18 and a celebration in Rome of the EU’s founding treaty on March 25.

Domestic Critics

The premier must first deal with her domestic critics. With a narrow majority of 17, her government is vulnerable to defeat in the House of Commons if as few as nine Tories rebel.

“The government is under serious pressure from its own benches to make a concession,” said James McGrory, co-executive director of the Open Britain campaign against a so-called hard Brexit. “That pressure could intensify over the weekend.”

The prime minister is already battling a revolt from Tories over her plan to increase taxes on the self-employed. That violation of a 2015 campaign pledge triggered a backlash that could embolden more Tory opposition on Brexit. Anna Soubry, another former minister, said the tax criticism showed Britain was “barmy,” arguing that the Conservatives’ real betrayal of the public was to break an election promise to keep the U.K. in the EU single market.

Ping-Pong

If May gets her way and the Commons votes to overturn the amendments on Monday, the bill will be sent back to the Lords to reconsider. The upper house could then choose to reinstate the amendments and send the bill back to the Commons again. This is the process known as “ping pong.”

The government has set aside time on three days next week for the “ping-pong” stage, although May’s team is confident she’ll get her law past Parliament without any amendments in time for her to meet her deadline.

The prime minister says the tweaks to the 137-word bill are unnecessary and would deprive her of maximum flexibility in the Brexit talks.

“European partners have made clear to me that they want to get on with the negotiations,” May said on Thursday. “So do I. It is time to get on with leaving the European Union.”