More than 100 Seattle Times journalists have signed a protest letter because of their publisher's decision to sponsor political adverts.

It is underwriting ads on behalf of >Rob McKenna, who is standing as the Republican candidate for the state of Washington.

And it is doing the same for the referendum 74 campaign that seeks to legalise same-sex marriage in the state.

The Times is one of the few remaining major city dailies in the United States independently operated and owned by a local family (the Blethens).

The journalists' protest letter warned the current publisher, Frank Blethen, that the ad campaigns threaten the newspaper's credibility with readers.

It said: "We strive to remain independent from the institutions we cover. We shine a light on the process from the outside. We are not part of the process. This ad threatens to compromise that integrity."

Times spokeswoman Jill Mackie responded by saying there was "not a newspaper publisher in the United States who is more respectful or supportive of journalists."

Both McKenna and Ref. 74 have been endorsed by the paper's editorial board, but the board is not involved in the ad campaign.

The company's decision to jump into the races as a political donor has drawn harsh criticism from several political experts and media commentators. And, of course, from the Democratic party.

Sources: Seattle Times/Wikipedia/Washington united for marriage