LONDON (AP) — British Prime Minister Rishi Sunak was trying to cajole recalcitrant lawmakers into supporting his signature immigration policy in a vote Tuesday, with defeat likely to leave his authority shredded and his government teetering.

The House of Commons is due to vote on whether to approve in principle a bill that Sunak says will revive a plan to send asylum-seekers to Rwanda that was ruled illegal by the U.K. Supreme Court.

Normally the vote would be a formality. Sunak’s Conservatives have a substantial majority, and the last time a government bill was defeated at its first Commons vote — known as second reading — was in 1986.

But the Safety of Rwanda (Asylum and Immigration) Bill faces opposition from hard-liners on the Conservative right, who say it does not go far enough to ensure migrants who arrive in the U.K. without permission can be deported.

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With opposition parties also saying they will oppose the bill, it would take fewer than 30 Conservatives to vote against the legislation to kill it.

Michael Tomlinson, the newly appointed minister for illegal migration, predicted that “this bill will get through tonight.” He promised to “engage constructively” with lawmakers to address their concerns.

Sunak invited more than a dozen hard-liners to a breakfast meeting in 10 Downing St. on Tuesday, trying to persuade them over coffee and smoked salmon. The group left without speaking to reporters.

If the bill passes Tuesday’s vote, weeks of wrangling and more votes in Parliament lie ahead before it can become law.

The Rwanda plan is an expensive, highly controversial policy that has not, so far, sent a single person to the East African country. But it has become a totemic issue for Sunak, 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 have done so this year, down from 46,000 in all of 2022.

Sunak believes delivering on his promise will allow the Conservatives to close a big opinion-poll gap with the opposition Labour Party before an election that must be held in the next year.

The plan has already cost the government 240 million pounds ($300 million) in payments to Rwanda, which agreed in 2022 to process and settle hundreds of asylum-seekers a year from the U.K. But no one has yet been sent to the country, and last month Britain’s top court ruled the plan illegal, saying Rwanda isn’t a safe destination for refugees.

In response, 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, regardless of the Supreme Court ruling.

The law, if approved by Parliament, would allow the government to “disapply” sections of U.K. human rights law when it comes to Rwanda-related asylum claims.

The bill has faced criticism from centrist Conservative lawmakers concerned that it sidelines the courts, though a major centrist faction, the One Nation group, said Monday that it would support the bill.

But legislators on the party’s authoritarian wing think the legislation is too mild because it leaves migrants some legal routes to challenge deportation, both in U.K. courts and at the European Court of Human Rights.

Human Rights groups have long argued that it’s unworkable and unethical to send asylum-seekers to a country more than 4,000 miles (6,500 kilometers) away, with no hope of ever returning to the U.K.

Sacha Deshmukh, chief executive of Amnesty International U.K., said “the Rwanda Bill will strip some humans of their human rights, just when they are most in need of them.”

“We are urging all MPs in the strongest terms to take a stand against this outrageous attack on the very concept of universal human rights,” Deshmukh said.