Transgender soldiers can continue to serve in the military while the government determines whether to continue allowing them to do so, Defense Secretary Jim Mattis announced Tuesday.

President Trump signed a directive on Friday that prevents transgender individuals from joining the military — giving Mattis authority over what to do with those already serving and ordering a study on how transgender soldiers affect military readiness, effectiveness and budget.

“Once the panel reports its recommendations and following my consultation with the secretary of Homeland Security, I will provide my advice to the president concerning of his policy direction. In the interim, current policy with respect to currently serving members will remain in place,” Mattis said in a statement.

Last year, a similar Pentagon-commissioned study found that paying healthcare costs for the military’s 1,300–6,600 active transgender soldiers would cost between $2.4 million and $8.4 million a year. Allowing them to serve would not affect military readiness, the study found.

That study took six months.

Trump’s directive also tells the Department of Defense to halt sex-reassignment procedures for military personnel except in cases where it is necessary to “protect their health.”

The new policy goes into effect on Jan 1, 2018.