FCC nominees Jessica Rosenworcel and Ajit Pai passed a key vote by the Senate Commerce Committee on Thursday, but Sen. Chuck Grassley will attempt to block their appointment when it goes for a full floor vote.

The Iowa Republican doesn't have a problem with the nominees themselves but is using the appointees as leverage to get the FCC to provide answers on what he calls the agency's "apparent rush" to approve LightSquared's waiver for its hybrid satellite-terrestrial LTE network.

"As a last resort to try to exhort more transparency and accountability from the FCC, I'll place a hold on consideration of the agency nominees on the Senate floor," Grassley said.

If Grassley's block is successful, the FCC could be left with just three acting commissioners after the start of next year. Former Republican commissioner Meredith Atwell Baker resigned from the agency earlier this year to take a lobbying job at Comcast, and Democratic commissioner Michael Copps formally announced his retirement this week.

The nominations are expected to be put on the Senate calendar soon, but a vote has not yet been scheduled.

Senate majority leader Harry Reid could file for cloture to overcome Grassley's objection. The cloture motion would require 60 votes to overcome the block. Rosenworcel and Pai have so far received broad bipartisan support.

Grassley wants the FCC to hand over information about why it granted conditional approval of LightSquared's network plans despite concerns about GPS interference expressed by the NTIA and other federal agencies.

Tests later found that LightSquared's proposed network caused widespread blackouts in GPS service, forcing the company to move to a different spectrum band and develop special filters for high-precision receivers still affected by its service.

The approval has been linked to campaign contributions to the Obama administration by LightSquared parent company Harbinger Capital Partners, which has denied the allegations.

LightSquared's purported fixes for the problem are still being tested. The FCC has said the venture-backed company will not be allowed to move forward with the launch of its network until it can prove it has addressed interference to GPS.

Some in the GPS industry say the issue is an insolvable physics problem and want LightSquared to move to spectrum located farther away from GPS bands.

LightSquared said Wednesday that independent tests showed that even sensitive high-precision GPS receivers could be made compatible with its network. The results were challenged by opponents to the company's plan.