One of President Donald Trump's biggest supporters in the U.S. Senate has now co-signed a letter with his Democratic counterpart demanding the president comply with a federal law he recently ignored.

On Friday night, Trump announced he was firing 18 inspectors general throughout various federal agencies, including the Departments of Defense, Labor, State and Health and Human Services. This was done in violation of the Inspector General Act, which requires that a president give Congress 30 days advance that he plans to fire an inspector general — which is an independent watchdog that calls out waste, fraud and abuse — and give a specific reason for their firing.

And on Tuesday, Senate Judiciary Committee Chairman Chuck Grassley (R-Iowa) and Ranking Member Dick Durbin (D-Ill.) both signed a letter to Trump, pointing out that the firings were illegal. Politico legal correspondent Kyle Cheney posted the full text of the letter to Bluesky."Congress was not provided the legally required 30-day notice and case-specific reasons for removal, as required by law," Grassley and Durbin wrote. "Accordingly, we request that you provide that information immediately."

"While IGs aren't immune from committing acts that require their removal, and they can be removed by the president, the law must be followed," they continued. "The communication to Congress must contain more than broad and vague statements, rather it must include sufficient facts and details to assure Congress and the public that the termination is due to real concerns about the inspector General's ability to carry out their mission."

In addition to providing rationale for their firing, both senators insisted that Trump reinstate the fired inspectors general on an "acting" basis during the 30-day period and "work quickly to nominate qualified and non-partisan individuals to serve in those open positions." Trump has not yet responded to the letter.

As chairman of the Judiciary Committee, Grassley is perhaps the most critical in implementing Trump's policies pertaining to immigration, which is under his purview. Grassley's committee will also have to vet all of Trump's nominees to the federal courts, including anyone he nominates to succeed retiring Supreme Court justices. And as a 91 year-old senator who isn't up for re-election until 2028, Grassley is virtually untouchable in the Hawkeye State, which he has represented for more than 40 years.