The British government’s contentious policy to stem the flow of migrants faces one of its toughest challenges this week as the U.K. Supreme Court weighs whether it’s lawful to send asylum-seekers to Rwanda. The Conservative government is challenging a Court of Appeal ruling in June that said the policy intended to deter immigrants from risking their lives crossing the English Channel in small boats is unlawful because the East African country is not a safe place to send them.

Three days of arguments are scheduled to begin Monday with the government arguing its policy is safe and lawyers for migrants from Vietnam, Syria, Iraq, Iran and Sudan contending it’s unlawful and inhumane. The hearing comes as much of Europe and the U.S. struggle with how best to cope with migrants seeking refuge from war, violence, oppression and a warming planet that has brought devastating drought and floods.

Prime Minister Rishi Sunak has vowed to “stop the boats” as a top priority to curb unauthorized immigration. More than 25,000 people are estimated to have arrived in the U.K. by boat as of Oct. 2, which is down nearly 25% from the 33,000 that had made the crossing at the same time last year. The policy is intended to put a stop to the criminal gangs that ferry migrants across one of the world’s busiest shipping lanes by making Britain an unattractive destination because of the likelihood of being given a one-way ticket to Rwanda.