President Barack Obama outlined a plan to close Guantanamo Bay in Cuba that he supports. It will be his last chance to close the controversial prison before he leaves the White House and sets up a new battle with Congress.

The plan lists 13 potential locations within the U.S. to transfer detainees to, officials said Tuesday, reports CNN. Congress, which is controlled by Republicans in both chambers, will have to approve the plan, but Republicans aren’t expected to. The specific locations proposed were not revealed.

Obama said that, in addition to the safe transfer of detainees, the closing process will include officials deciding which detainees would stand military trials. Most of the detainees would be moved to other countries, but others who cannot be transferred will go to a facility in the U.S.

“This plan has my full support,” Obama said. The president, who declared during his first run for the Oval Office that he would close the prison, admitted that the process has been difficult. “If it were easy, it would have happened years ago,” he added, reports USA Today.

An official told Reuters that closing the prison and transferring the prisoners will cost between $290 million and $475 million. But the cost would be offset in three to five years, since housing the detainees in the U.S. instead of Cuba will be cheaper. There are still 91 detainees in Guantanamo Bay and 35 of them can be transferred to other countries.

Republicans have insisted that detainees not be transferred to facilities on U.S. soil. Arizona Sen. John McCain called the plan a “vague menu of options” and “not a credible plan” for closing Guantanamo.