Sen. John Thune, R-S.D., chairman of the U.S. SenateCommittee on Commerce, Science and Transportation, questioned CEO Mark Zuckerberg overa report that claimedthe social networking giant was stopping conservative news stories fromappearing in its Trending Topics section, according to a May 10 news release.

In a letter sent to Zuckerberg, Thune sought an explanationfor the "serious allegations," and asked if the company was takingany steps to investigate and hold the responsible individuals accountable.

The move comes after Facebook executive Tom Stocky rejecteda Gizmodo reportthat made the allegations of politically motivated manipulation of news storiesin the Trending Topics section.