House Oversight and Reform Committee Chairman Elijah Cummings (D-Md.) sent letters Tuesday calling for eight current and former Trump administration officials to provide information for two of the panel’s investigations, cautioning that officials who block the interviews from taking place could see their salaries withheld.

“Please be advised that any official at the Department who ‘prohibits or prevents’ or ‘attempts or threatens to prohibit or prevent’ any officer or employee of the Federal Government from speaking with the Committee could have his or her salary withheld pursuant to section 713 of the Financial Services and General Government Appropriations Act,” Cummings wrote in the letters.

The move is the latest in an escalating power struggle between the Trump administration and House Democrats over investigations. Tensions between the White House and congressional Democrats have amplified in recent weeks, with President Trump telling reporters last month that he plans to fight “all the subpoenas.”