More than a dozen retired top military commanders, leaders and advisers, whose careers spanned both Republican and Democratic administrations, are throwing their weight behind a bill in the House and Senate that would require universal background checks for all U.S. gun sales.

In a letter Thursday, 13 former top military advisers and combat leaders urged congressional leaders in both parties to pass the bill, known in the House as HR 8, which targets private gun sales that don’t require background checks under current federal law.

“A prohibited person with dangerous intent can easily buy a gun over the internet or in a parking lot with no questions asked,” the military advisers wrote to Speaker Nancy Pelosi, House Minority Leader Kevin McCarthy, Senate Majority Leader Mitch McConnell and Senate Minority Leader Charles E. Schumer.“For those of us with extensive firearms training, who have seen the damage inflicted by a powerful weapon in the wrong hands, this is simply unfathomable,” they wrote.

The list of heavyweight signatories includes former NSA and CIA director Michael Hayden, who served under Presidents Bill Clinton, George W. Bush and Barack Obama; Stanley McChrystal, Obama’s top commander in Afghanistan; and former Coast Guard Commandant Thad Allen, who served under both Bush and Obama.

McChrystal is a member of Roll Call parent company FiscalNote’s board of directors.