Republican efforts in the House to pass a budget have been stymied for weeks by members who say they want to attack so-called “mandatory spending”—autopilot outlays such as Medicare, Social Security and other similar programs.

But on Tuesday, Rep. Mac Thornberry (R-Texas), chairman of the House Armed Services Committee, said the fact that one controversial proposal—making women register for the Selective Service System—was mandatory in nature meant it had to be tossed from his defense policy bill.

Rep. Mac Thornberry

In 2011, when Republicans took control of the House, Republicans put in place a “cut-go” rule: Spending for a mandatory program could not increase unless a similar cut was made elsewhere. The rule was meant to provide political cover for eliminating the pay-go rule imposed by Democrats, which said a mandatory program boost or tax cut had to be offset elsewhere so the combination didn't add to the deficit.

“Mandatory savings is generally a good thing,” Thornberry told reporters after House Republicans held their weekly policy meeting. “On the other hand, in this case, the mandatory savings ruling from CBO was somewhat of a surprise.”

Thornberry said the Congressional Budget Office reasoned that some women would likely not register with Selective Service and thus forfeit eligibility for federal student aid, some of which is counted on the mandatory spending side of the ledger. Debating whether to amend the provision violates House rules, he said, because cut-go forbids debate on proposals that boost mandatory spending by themselves.

“If it prevents us from even discussing an issue—such as women in Selective Service—then I think we need to take a step back. If it were up to me, I would probably take a look at the rules that prevent us from even discussing an issue like this,” he said.

To get around that, Thornberry said, the procedural rule getting the defense bill to the House floor includes a self-executing change in the bill that will alter the current provision to one that would only require a study of registering women with Selective Service.

Thornberry said there would be increased expense in having women register and he didn't know if the higher spending for that—on the annual discretionary spending side—would outweigh savings on the mandatory side.