The decision deals the biggest legal blow to the Selective Service System since the Supreme Court upheld  the draft registration process in 1981. In Rostker v. Goldberg, the court ruled that a male-only draft was "fully justified" because women were ineligible for combat roles.

But U.S. District Judge Gray Miller ruled late Friday that while historical restrictions on women serving in combat "may have justified past discrimination," men and women are now equally able to fight. In 2015, the Pentagon lifted all restrictions for women in military service. 

The case was brought by the National Coalition For Men, a men's rights group, and two men who argued an all-male draft was unfair.

Men who fail to register with the Selective Service System at their 18th birthday can be denied public benefits such as federal employment and student loans. Women cannot register for Selective Service.