Grassley stressed that Clinton was "extremely careless" with the classified documents.
"I have repeatedly asked the State Department whether Secretary Clinton and her associates had their clearances suspended or revoked to which the Obama Administration refused to respond," Grassley wrote in a Thursday letter to US Secretary of State Rex Tillerson, as quoted by Fox News.
The US Federal Bureau of Investigation (FBI) has conducted a criminal investigation of Tillerson's predecessor, Hillary Clinton, on whether she intended to violate US laws by using a private email server and electronic devices for official business during her tenure as secretary of state in 2009-2013.
According to Grassley, any US government workers who have somehow managed to retain access to top-secret information after leaving the State Department must have their clearances suspended pending an investigation.