(NewsNation) —  A U.S. senator who’s worked to protect whistleblowers within the federal government wants to make sure workers know just how well they’re protected.

“The importance of whistleblowers knowing their rights under the law cannot be stated enough,” wrote Sen. Chuck Grassley, R-Iowa, in letters to the inspectors general of 74 federal agencies.

Grassley says some federal agencies have illegally omitted “anti-gag” language from their nondisclosure agreements. Federal law requires those deals to let workers know about their rights to report waste, fraud or abuse.

“Federal agencies cannot be allowed to conceal their wrongdoing behind illegal non-disclosure policies and related actions,” Grassley wrote.

The letter caps Grassley’s work during “Sunshine Week,” an annual collaboration of government, private business, journalists and others to reinforce the importance of open government.

“Whistleblowers are patriots and our most powerful tool in rooting out waste, fraud, abuse and misconduct,” Grassley said in a speech Monday on the Senate floor. “Despite their vital contribution to good government, they’re often targeted for retaliation and harassment. That should stop.”

Grassley’s reputation as an advocate for whistleblowers put him deep into the the case of Alexander Smirnov, the former FBI informant who’s now charged with lying about bribery allegations against President Joe Biden.

Last year, Grassley publicly released an internal FBI document leaked by what he called a “whistleblower.” It contained unconfirmed claims that the CEO of the Ukrainian energy company Burisma paid a $10 million bribe to the Bidens.

Republicans often used the document to bolster calls for the impeachment of Biden and the discrediting of his son, Hunter. “That to me is really the heart of this matter,” Judiciary Committee Chairman Rep. Jim Jordan, R-Ohio, told Fox News in January.

Last month, FBI agents arrested Smirnov on charges of lying to the FBI and creating a false record to back up his Biden story. He’s currently in jail over concerns he could flee the U.S. before his trial.

After Smirnov’s arrest, Grassley told reporters it was his release of the unconfirmed FBI document that led the bureau to look closer at Smirnov.

“Just think of what I did for the people this country for making sure that somebody was misleading the FBI is no longer going to mislead them,” Grassley told Iowa reporters in February. “And think what I did for the people of this country to make sure that the FBI is doing its job.”