Defense Secretary Ash Carter is expected to order the military to open all combat jobs to women today, giving the services until January 1 to submit plans to make the change, according to the Associated Press.

More than 200,000 women serve in active duty, according to Pentagon figures from 2011. Most of those women work in the medical and administrative specialties. A senior defense official, speaking on condition of anonymity, told the AP that all services will have to begin putting plans in place for combat integration by April 1.

In January 2013, then-Defense Secretary Leon E. Panetta lifted the official Pentagon ban on women in combat, which had been enacted in 1994 and prevented women from serving in artillery, armor, infantry, and other combat roles. The move made a quarter million jobs available to women, according to the Marine Times.

Even as some parts of the military sought to make the change, others resisted. The commandant of the Marine Corps in September recommended that women be excluded from certain front line combat jobs, citing studies that claimed male-only units perform better than gender-integrated units, and that women have higher injury rates than men.

Serving in combat positions is crucial to career advancement in the military, according to advocates of removing the ban.

“Many of the positions currently banning women are necessary for career development and success,” a spokesperson for the Service Women’s Action Network (SWAN) told The Muse. “SWAN has dubbed this the ‘brass ceiling’ that the combat exclusion policy places over women’s advancement in the Armed Services.”