Other than basic factual accuracy, there may be no principle of journalistic ethics more sacred than disclosure of conflicts of interest. On op-ed pages it is understood that the writers have no commitment to neutrality. But it is also a given that a reader cannot evaluate the arguments if she is unaware of a personal stake writers have in the subject at hand.

A perfect example of this came in Friday’s Wall Street Journal, which published an op-ed by former Senator Evan Bayh. The piece complains about the medical device tax in the Affordable Care Act, which is a strange fixation for an elder statesman. As Jonathan Chait points out in New York magazine, the explanation comes in Bayh’s bio, which notes that Bayh “is a partner at the McGuireWoods law firm, which represents several medical-device companies.”

So The Journal, its conservative corporatist politics notwithstanding, seems to understand the importance of disclosing such information.

And yet they almost never do it when the writer is an adviser to Mitt Romney’s presidential campaign. On Tuesday, for example, The Journal published an op-ed by Michael Mukasey making the ludicrous and unsubstantiated assertion that President Obama may release the mastermind of the 1993 attack on the World Trade Center. Mukasey was identified as a former US Attorney General and federal judge.

As Media Matters noted, Mukasey is also an adviser to the Romney campaign, an extremely relevant fact that went unmentioned. A reader of the piece would have no idea that Mukasey has a strong professional incentive to spread bogus rumors about Obama, since he is working for his opponent.

This is not an isolated incident. Media Matters has been tracking this unethical practice by The Journal, and has found nine previous op-ed writers who are Romney campaign advisers but were not identified as such. A week before the Mukasey piece ran, Media Matters wrote,

The Journal published a total of twenty-three pieces from the following Romney advisers without disclosing their campaign ties: John Bolton; Max Boot; Lee A. Casey; Paula Dobriansky; Mary Ann Glendon; Glenn Hubbard; Michael Mukasey; Paul E. Peterson; David B. Rivkin Jr.; and Martin West. In several instances, the Journal failed to disclose an op-ed writer’s connection despite its own news section reporting that the writer is advising Romney.

Editorial page editors at other newspapers are aghast at The Journal’s practice, calling it “shameless” and “inexcusable.”

Nor is The Journal’s unethical practice limited to those ten writers. The Journal also runs a weekly column by Karl Rove. Rove analyzes the campaign, and he has never been identified as a player in the campaign himself, even though his political action committees have raised and spent tens of millions of dollars on behalf of Republican candidates.

Last week, The Journal finally acknowledged in his bio line that Rove is the cofounder of American Crossroads. It is unknown if this was in response to criticism, and whether it constitutes a new policy. The Journal has not responded to repeated requests for comment from Media Matters and they had not responded to a request from The Nation at the time of this writing.

While The Journal’s behavior is unusual and embarrassing for a respected broadsheet newspaper, it is par for the course within the conservative media. Fox News has many contributors, such as John Bolton, who criticize Obama on their programming without being identified as a Romney campaign adviser or employee. (Rove is also a Fox News contributor.)

There is nothing wrong with Fox or The Journal editorial section being openly conservative. But if their contributors are working on behalf of a vested interest, such as the Romney campaign, their readers and viewers deserve to know.

The Wall Street Journal featured another controversial op-ed today, in which Mitt Romney fanned anti-Muslim flames. Check out Robert Dreyfuss’s coverage here.