By Alina Selyukh

WASHINGTON (Reuters) - Republican Senator Ted Cruz, a conservative whose defiant stand against Obamacare helped prompt the U.S. government shutdown, has blocked the Senate from voting on the nomination of Tom Wheeler to be Federal Communications Commission chairman.

The Senate was scheduled to vote on Wheeler, a Democrat and telecom industry veteran, late on Wednesday. Cruz held up the vote over questions about the FCC's power to enforce disclosures of who sponsors political television advertising.

"The Senator is holding the nominee until he gets answers to his questions regarding Mr. Wheeler's views on whether the FCC has the authority or intent to implement the requirements of the failed Congressional DISCLOSE Act," said Cruz spokesman Sean Rushton, referring to a failed bill meant to step up political disclosures.

"Mr. Wheeler had previously declined to give specific answers, but as he's now expressed his readiness to revisit the Senator's questions, the Senator hopes to communicate with him soon," Rushton said.

If Wheeler cannot resolve Cruz's concerns, Senate Democrats could force a vote on the nomination. Majority Leader Harry Reid would decided whether to take that action.

Clearing the senator from Texas' procedural roadblock would require 60 votes in the 100-member chamber, meaning the support of some Republicans would be needed. Democrats currently hold 52 seats and usually have the support of two independent Senators.

The Senate also has yet to vote on the nomination of Republican Michael O'Rielly to fill the fifth and final open FCC commissioner position.

Cruz, prominent in the small-government Tea Party wing of his party, had threatened earlier to delay Wheeler's confirmation vote after pressing for a more detail from the nominee on his views of the donor disclosure issue.

As political spending by outside advocacy groups pushes into the billions of dollars each election cycle, voters are exposed to a growing deluge of ads that refer to the often vaguely named groups sponsoring them.

Story continues

Some Democrats have suggested that the FCC's existing oversight authority over broadcasters could also be used to force TV advertisers to name specific funders for each spot they buy. That idea has emerged as Cruz's focus at the Senate Commerce Committee, which oversees the commission.

The FCC remains in something of a holding pattern under Acting Chairwoman Mignon Clyburn. It awaits Wheeler's confirmation to move ahead on several key projects, including upcoming auctions of spectrum. Former chief Julius Genachowski left the FCC in May.

The agency also saw its operations, including approvals of new device licenses and acceptance of routine required filings, stalled by the government shutdown that started on October 1 and ended late on Wednesday. All but a few dozen of the FCC's roughly 1,700 workers were furloughed.

Wheeler most recently invested in technology at a venture capital firm, raised money for President Barack Obama's political campaigns and advised Obama and the FCC on telecom issues. In the past he has been an industry lobbyist, running the National Cable Television Association and the wireless industry group CTIA.

O'Rielly, the Republican FCC nominee, has spent nearly two decades as a staffer in Congress, most recently serving as a top aide to Senator John Cornyn of Texas.

(Reporting by Alina Selyukh; Additional reporting by Tom Ferraro; Editing by Ros Krasny and Tim Dobbyn)