A local union has questioned Ed O'Reilly's "working class guy" campaign persona, charging that O'Reilly has neglected to hire unionized workers.

In a letter to O'Reilly (D-Gloucester) earlier this week obtained by PolitickerMA.com on Friday, the local chapter of the International Union of Painters and Allied Trades, a branch of the AFL-CIO, sharply criticized O'Reilly for not hiring unionized painters to paint his campaign office.

"You have made efforts to reach out to organized labor and yet when you painted your campaign office in Amherst, you chose to hire a non-union painter," the letter, which is dated Aug. 4, states. "This action can do little more than raise the question of whether or not you are sincere in your pronouncements to support the issues important to working class men and women in this country."

"How can you proclaim your support for unions," the letter goes on, "and then not feel it necessary to hire union workers yourself?"

O'Reilly is challenging U.S. Sen. John Kerry (D-Boston) in this year's Sept. 16 Democratic primary. The union that sent the letter has endorsed Kerry in this year's Senate race.

The letter, signed by John Laughlin, the union's director of political and public relations, also calls for O'Reilly to release his tax returns for the last five years to the public.

"Repeatedly, you have referred to yourself as a ‘working class guy' and you have made a point of highlighting why you dislike John Kerry and where the two of you disagree on certain policy areas," the letter states, "But frankly, that is not enough."

The Kerry campaign said the senator has filed a federal financial disclosure form to the Secretary of the Senate every year, as is required of every senator, but he has not made his tax returns public since running for president in 2004.

At the time of the publication of this story, the O'Reilly campaign had not returned a call or an e-mail for comment.

Laughlin said in an interview that the union flipped through O'Reilly's Federal Election Commission report and saw that he had spent money on painting his western Massachusetts campaign headquarters. The union looked into it, and found that he had not hired unionized workers.

The union originally planned to picket the headquarters, but when O'Reilly closed it, Laughlin decided to mail a letter. Laughlin said he has received confirmation that the letter was delivered to O'Reilly's law office.

The issue, Laughlin said, is transparency.

"It just struck me that if we‘re going to talk about disclosure then disclosure is important all around," he said. "If my members are going to consider someone to vote for, it seems fair to us that you should put all the cards on the table."