LONDON (AP) — U.K. Prime Minister Rishi Sunak faces a test of his authority and his nerve on Wednesday as he tries to subdue a Conservative Party rebellion and win parliamentary approval for his stalled plan to send some asylum-seekers on a one-way trip to Rwanda.

Lawmakers are due to vote on a bill that aims to overcome a U.K. Supreme Court block on the Rwanda plan, a day after some 60 members of Sunak’s governing Conservatives rebelled in an effort to make the legislation tougher. The dissent cost Sunak two party deputy chairmen, who quit in order to vote against the government on the amendments. A junior ministerial aide also resigned.

A similar rebellion on Wednesday would doom the Safety of Rwanda Bill, and potentially Sunak’s 15-month-old government.

Sunak has made the controversial — and expensive — immigration policy central to his attempt to win an election this year. To do that he needs to unite the Conservatives, who trail far behind the Labour opposition in opinion polls. But the liberal and law-and-order wings of the Conservatives — always uneasy allies — are at loggerheads over the Rwanda plan.

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Moderates worry the policy is too extreme, concerns underscored when the United Nations’ refugee agency said this week the Rwanda plan “is not compatible with international refugee law.”

However, many on the party’s powerful right wing think the bill doesn’t go far enough in deterring migration to the U.K. Hard-liners’ attempts to toughen the bill by closing down avenues of appeal for asylum-seekers failed Tuesday, and some of the Conservative rebels say they will oppose the legislation as a whole if it is not strengthened. If about 30 Tory lawmakers oppose the bill, it could be enough, along with opposition votes, to kill the legislation.

But many Conservative lawmakers may hesitate to take the nuclear option of killing Sunak’s signature policy, a move that could trigger panicky moves to replace him or even spark a snap election. The government has to call a national election by the end of the year.

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.

Illegal Immigration Minister Michael Tomlinson said there was only an “inch of difference” between the government and its Conservative critics, and “actually we all want the same thing.”

He said he was confident the bill “is going to get through tonight.”

The Rwanda policy is key to Sunak’s 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 during 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.