The U.S. Park Police (USPP) has seen staffing levels drop and a strain on resources behind the scenes as one of the country's oldest law enforcement agencies continues to ask for more resources, according to union leaders.

The agency, which primarily safeguards national monuments in Washington, D.C.; New York City; and San Francisco, is at its lowest staffing level since 1975, according to Ken Spencer, chairman of the United States Park Police Fraternal Order of Police (FOP).

"At the officer level, it feels like it's almost deliberate, how bad they let our staffing get," he told Fox News Digital . "Days off are always canceled. Leave is canceled frequently. And the day-to-day operations [are] just absolutely unsafe for the mission that we have."

"In 1975, the U.S. Park Police had a total of 547 sworn officers nationwide," Spencer told Fox News Digital. "Today, we have 515, and that number continues to shrink. Despite our best efforts for years to highlight our critical staffing concerns, Congress, the Department of Interior and the National Park Service have not made any reasonable effort to address this crisis."

"Our officers want the American people to know that there’s a draft bill in Congress that would fix our staffing crisis for decades to come," Spencer said. "Unfortunately, both parties have neglected the agency and the bill sits dormant. We hope this recent event will encourage members of Congress to force the Interior Department and the National Park Service to finally address this serious shortcoming in federal law enforcement. Immediate action is needed to ensure the safety of our officers and the public we serve."