Rep. Ed Markey’s U.S. Senate campaign has started to air ads on Channel 5, a station fellow Democratic Rep. Stephen Lynch has declined advertise with due to an apparent union contract dispute. The Markey campaign’s ads started this weekend.

Sixty camera operators, editors and technicians with IBEW Local 1228 have been working under an extended contract since 2011. Earlier this month, Lynch, a former union president who is vying for the Democratic nomination, said he could not in “good conscience spend hundreds of thousands of dollars advertising on WCVB while IBEW members have gone nearly two years without a new contract.”

Asked about the ad buy, Giselle Barry, a Markey spokeswoman, said on Friday that the campaign will take the union’s concerns into consideration as they develop an advertising plan and hopes both parties will bring about a resolution to the situation.

Whether there has been a contract dispute is in dispute: According to an Associated Press write-up, WCVB President Bill Fine claimed that a contract dispute doesn’t exist and there are tentative agreements in place.

The union hit back in a statement earlier this month. "The statements by Bill Fine paint a rosy picture of negotiations which is inaccurate," the union said. "Mr. Fine has not been at the bargaining table. When we met for negotiations last week, we asked the Company representatives how we were to explain the Company’s proposal, justifying why over 24 members of the shop should take a 15% pay cut while the Company is enjoying record profits and WCVB is enjoying great ratings. We were told ‘That's your job, we're not going to tell you how to present this to the membership.’"

The head of the Massachusetts AFL-CIO, Steve Tolman, sent an email this week asking fellow union members to stand behind IBEW members at Channel 5.

Contenders for the U.S. Senate seat, which opened up after John Kerry decamped for the State Department, will face off next week at Channel 5’s Needham studios. The Republicans – Gabriel Gomez of Cohasset, former U.S. Attorney Michael Sullivan and state Rep. Dan Winslow – will debate for 30 minutes. The Democrats, Lynch (D-South Boston) and Markey (D-Malden), will also debate for 30 minutes.

New England Cable News’ R.D. Sahl is set to moderate the debates, which are scheduled for Wednesday, March 27, at 7 p.m. and produced by a Boston media consortium.

UPDATE: This post was updated at 1:11 p.m. with a past statement from IBEW union at Channel 5.