"Given your pledge on October 28, I was disappointed to learn yesterday that Mr. de Sa was 'not available' to be interviewed by my staff," Grassley wrote. He asked Genachowski to make de Sa available before Jan. 31.
Grassley is the top Republican on the Judiciary Committee, but he does not sit on the Commerce, Science and Transportation Committee, which has jurisdiction to oversee the FCC.
LightSquared has invested billions of dollars to launch a nationwide wireless broadband service, but tests have shown its planned network could interfere with GPS devices. The FCC granted the company a conditional waiver last year, but officials say the company will not receive final approval to launch its network until it can demonstrate it has fixed the interference problem.
Grassley and other Republicans have questioned why the FCC allowed LightSquared to get as far as it has in the regulatory process. The senator has pledged to block President Obama's two nominees to the FCC unless the agency releases internal records related to its review of LightSquared.
Paul de Sa met with LightSquared officials, including billionaire investor Phil Falcone, earlier this month.
Grassley brushed off accusations that his requests from the FCC are a "witch hunt."
“Asking to meet with the ‘father’ of this project before he leaves the agency in a few weeks is due diligence, not a witch hunt," Grassley said in a statement. "Besides, if this top FCC official has time to meet with the hedge fund owner behind LightSquared, he should have time for a meeting with Senate staff trying to shed some light on a controversy created at the FCC.”
The FCC did not immediately comment on Grassley's request to meet with de Sa.
--Updated at 4:43 p.m.