Now that the Pentagon permits women to hold any position in the military, including on the front lines of war, Congress has taken up the debate over whether they should also be required to register for the draft.

On Tuesday, the Senate approved a military spending bill that requires women to be registered for mandatory military service when they turn 18. The sweeping bill, which authorizes $602 billion in additional military spending, passed with broad bipartisan support. But some conservative Republicans voted against it because of the provision requiring women register for Selective Service.

Texas Senator Ted Cruz was one of those Republicans.

"It is a radical change that is attempting to be foisted on the American people," Cruz said in a statement. "The idea that we should forcibly conscript young girls into combat, to my mind, makes little or no sense."

But most other lawmakers supported the change.

"The fact is, every single leader in this country, both men and women, members of the military leadership," said Republican Senator John McCain, who is also the chairman of the Armed Services Committee which drafted the provision, "believe that it's fair since we opened up all aspects of the military to women that they would also be registering for Selective Services."

Texas Senator John Cornyn also supported the change, saying, "if women are going to have an equal role in society to men... that national service ought to be an area where they would be expected to register."

Women have historically been exempt from the draft because they were barred from serving in combat positions. But last December, Defense Secretary Ash Carter opened up all military combat roles to any gender, removing any justification for limiting the draft to only men, argued the Senate Armed Services Committee in their summary of the bill.

According to the language in the senate's bill, women who turn 18 after January 1, 2018 will have to register for Selective Service, just like their male counterparts. It should be noted, though, that just because they're registering, doesn't mean that they will be enlisted — the last time the US used the draft was more than four decades ago during the Vietnam War.

The head of each military branch expressed support for the expanded draft requirements in their testimony to the committee.