LONDON (AP) — A key plank in the British government’s plan to send some asylum-seekers on a one-way trip to Rwanda is expected to become law this week, but opponents plan new legal challenges that could keep deportation flights grounded.

A bill aimed at overcoming a U.K. Supreme Court block on sending migrants to Rwanda is expected to pass Parliament this week after the government overcomes efforts to water it down in the House of Lords.

The Rwanda plan is key to Prime Minister Rishi Sunak ’s pledge to “stop the boats” bringing unauthorized migrants to the U.K., and Sunak has repeatedly said the long-delayed first flights will take off by June.

It has been two years since Britain and Rwanda signed a deal that would see migrants who cross the English Channel in small boats sent to the East African country, where they would remain permanently. The plan has been challenged in the courts, and no one has yet been sent to Rwanda under an agreement that has cost the U.K. at least 370 million pounds ($470 million).