At least 12 others refuse to say what they will do in that regard, The Hill, a Washington political newspaper, reported Thursday.
Many of the recalcitrant GOP lawmakers won't give a reason for their stand. Rep. John Peterson, R-Pa., had major concerns about McCain's energy policies and Rep. Walter Jones, R.-N.C., mentioned the Iraq war.
Some say that while they are not endorsing the presumptive GOP presidential nominee, that doesn't mean they don't support the veteran Arizona senator.
Throughout his career in both houses, McCain has been at odds with his party on a range of issues, including campaign finance reform, immigration, healthcare, taxes and energy.