Seven House Democrats are asking the Biden administration to make COVID-19 vaccines mandatory for service members, calling unvaccinated troops “a critical threat to our national security and public health,” Navy Times reports.

In a letter sent this week to the White House, the lawmakers said giving service members a choice to opt out is “contrary to the best interests of service members, their families, communities and colleagues.”

The letter was written by Rep. Jimmy Panetta (D-Calif.) and was also signed by Reps. Cindy Axne (D-Iowa), Jahana Hayes (D-Conn.), Sara Jacobs (D-Calif.), Marilyn Strickland (D-Wash.) and Marc Veasey (D-Texas), CNN reports.

Military leaders told Congress last month that about one-third of service members had declined to get the vaccine at that point.

Air National Guard photo by Senior Airman Ryan Mancuso