Chelsea Clinton appearing in an ad endorsing Referendum 74 in Washington state was blocked from being used by NBC News.

Passage of the ballot initiative allows a gay marriage law approved by lawmakers to take effect on December 6.

(Related: Seattle City Hall to open Sunday, December 9 for first gay weddings.)

According to BuzzFeed.com, Clinton starred in a video supporting Referendum 74, as well as a second broader video in which she endorsed marriage equality. The second video supposedly was intended to shore up efforts in three other states where the issue was on the ballot: Maine, Maryland and Minnesota.

The campaign was “scuttled” by NBC, Clinton's employer, an anonymous source is quoted as saying. A previous The New York Post story cited Clinton's NBC News contract as preventing her from campaigning for President Barack Obama's reelection campaign.

Clinton, along with her famous father, President Bill Clinton, visibly campaigned for passage of marriage equality in New York last June. She joined NBC News as a “special correspondent” last November. Clinton's reporting at the network avoids politics.