LONDON (AP) — U.K. Prime Minister Rishi Sunak faces rebellion from senior lawmakers in his Conservative Party over his stalled plan to send asylum-seekers on a one-way trip to Rwanda, a controversial and expensive policy that the British leader has made central to his attempt to win an election this year.

To do that he needs to unite his fractious party, which trails far behind the Labour opposition in opinion polls. But the liberal and authoritarian wings of the Conservatives — always uneasy allies — are at loggerheads over the Rwanda plan. Moderates worry the policy is too extreme, while many on the party’s powerful right wing think it doesn’t go far enough.

In a blow to Sunak, two deputy chairmen of the Conservative Party say they will vote to toughen up the government’s flagship Safety of Rwanda Bill in the House of Commons on Tuesday. Lee Anderson and Brendan Clarke-Smith announced they will back amendments seeking to close down asylum-seekers’ avenues of appeal against deportation to Rwanda.

“I want this legislation to be as strong as possible,” Clarke-Smith wrote on X, formerly known as Twitter.

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More than 60 Tory lawmakers, including former Prime Minister Boris Johnson, support amendments to toughen the legislation, and some say they will vote against the bill as a whole if it is not strengthened. Along with opposition party votes, that might be enough to kill the legislation. That would be a major blow to Sunak’s authority and potentially fatal to the Rwanda plan.

Sunak insists the bill goes as far as the government can because Rwanda will pull out of its agreement to rehouse asylum-seekers if the U.K. breaks international law.

Conservative moderates, meanwhile, worry the bill already flirts with breaking international law and say they will oppose it if it gets any tougher. Those concerns were underscored by the United Nations’ refugee agency, which said Monday that, even with the treaty and new legislation, the Rwanda plan “is not compatible with international refugee law.”

Sunak has made the Rwanda policy central to his pledge to “stop the boats” bringing unauthorized migrants to the U.K. across the English Channel from France. More than 29,000 people made the perilous journey in 2023, down from 42,000 the year before. Five people died on the weekend while trying to launch a boat from northern France in the dark and winter cold.

London and Kigali made a deal almost two years ago under which migrants who reach Britain across the Channel would be sent to Rwanda, where they would stay permanently. Britain has paid Rwanda at least 240 million pounds ($305 million) under the agreement, but no one has yet been sent to the East African country.

The plan has been criticized as inhumane and unworkable by human rights groups and challenged in British courts. In November the U.K. Supreme Court ruled the policy is illegal because Rwanda isn’t a safe country for refugees.

In response to the court ruling, Britain and Rwanda signed a treaty pledging to strengthen protections for migrants. Sunak’s government argues that the treaty allows it to pass a law declaring Rwanda a safe destination.

If approved by Parliament, the law would allow the government to “disapply” sections of U.K. human rights law when it comes to Rwanda-related asylum claims and make it harder to challenge the deportations in court.

If the bill is passed by the House of Commons on Wednesday, it will go to the House of Lords, Parliament’s upper chamber, where it faces more opposition.