The letter comes after Udall accused the Department of Interior last week of refusing to answer an inquiry from lawmakers about Trump's Independence Day plans, including how the additional cost of the plans will be covered.

The Washington Post reported last week that the National Park Service had redirected $2.5 million from its overall budget to help pay for the "Salute to America" event. Trump, flanked by supporters and Pentagon officials, spoke for roughly 45 minutes, focusing largely on the U.S. military.