While the letter stressed that the lawmakers do not believe the Senate will approve similar language, it said, "we think it would be the best course for you to reaffirm your strong support of the end of "Don't Ask, Don't Tell" by making it explicit that you would veto a bill in the unlikely event that it came to you."

The NDAA, which the House approved in late May by a 322-96 vote, includes language that would require the military to submit a written certification to Congress that repealing "don't ask, don't tell" (DADT) would "not degrade the readiness, effectiveness, cohesion, and morale" of U.S. armed forces. Critics of this language see it as a way of delaying the 2010 law that requires the military to abandon DADT as a policy.

In another section of the bill, Congress "reaffirms" the Defense of Marriage Act, and says that any reference to "marriage" within the military "means only a legal union between one man and one woman.

The Obama administration has said it "strongly objects" to the inclusion of language that seeks to delay the repeal of DADT, as prescribed by the 2010 law. However, the administration has not said it would veto the bill over this issue, as Frank asked.

Also signing the letter to Obama were Reps. Tammy BaldwinTammy Suzanne BaldwinMcConnell: Midterms will be 'very challenging' for GOP Vukmir gets boost with Wisconsin Senate GOP primary endorsement  GOP senate candidate dismisses 'fake outrage' over remarks against Democratic veterans MORE (D-Wis.), Jared Polis (D-Colo.), and David Cicilline (D-RI).