Anthony Brown kicks off his campaign for Maryland governor in May. (Photo by Astrid Riecken For The Washington Post)

As things stand now, Maryland Lt. Gov. Anthony G. Brown (D) should have a big advantage as he seeks the endorsement of the AFL-CIO, one of the most sought-after backers in the 2014 governor’s race for Democrats.

That’s because Brown is the only candidate to have qualified for consideration by the Maryland chapter of the labor organization.

Under new rules adopted this year, the AFL-CIO has said it will only consider endorsing statewide candidates that filed with the Board of Elections by the close of business on Thursday.

Brown’s two Democratic primary opponents — Attorney General Douglas F. Gansler (D) and Del. Heather R. Mizeur (D) — weren’t able to do so because neither has named a running mate. Under Maryland law, candidates for governor and lieutenant governor must file as a ticket by February.

After both the Gansler and Mizeur campaigns raised objections, Fred D. Mason Jr., president of the Maryland State and District of Columbia AFL-CIO, said Thursday afternoon that the new policy would be reevaluated.

“We’ll probably have more to say about that next week,” Mason said.

Earlier in the day, Mason defended the rule, which he said the gubernatorial campaigns were told about two months ago. The filing requirement, he said, was meant to demonstrate that candidates are committed to running and to prevent surprises.

Mason cited the group’s early endorsement of Democrat Kathleen Kennedy Townsend in the 2002 gubernatorial election. Afterward, she named a former Republican as her running mate.

Justin Schall, Brown’s campaign manager, said he had no problem with the AFL-CIO’s new policy.

“It is certainly understandable why they would want to know who is on the ticket in light of what happened in 2002,” Schall said, adding that Brown is “proud of his past partnerships with labor and looks forward to earning their support in this election and working with them in the future.”

Doug Thornell, a strategist for Gansler, said his campaign considered the rule change “truly disappointing.”

“This inexplicable change in the rules and precedent will deny AFL-CIO member organizations and the working folks they represent a choice when it comes to picking the next governor of Maryland,” he said. “Now they get one candidate; that’s not a choice.”

Joanna Belanger, Mizeur’s campaign manager, said she encourages AFL-CIO leaders to “look to their members for guidance here.”

“I sense many would not want their leadership to lock out any candidate with a strong labor background from the endorsement process months before the state-required filing deadline,” Belanger said.

Brown, who announced his campaign in May, named Howard County Executive Ken Ulman (D) as his running mate in June. The pair filed their paperwork at the state board last week.

Mason said the same filing requirement applies to candidates for attorney general and comptroller — which might explain a flurry of activity at the state board in recent days.

Comptroller Peter Franchot (D) filed for reelection on Thursday. And two candidates for attorney general — Dels. C. William Frick (D-Montgomery) and Aisha N. Braveboy (D-Prince George’s) — have filed within the past two days.

“I definitely wanted to be a part of their process,” Frick said of the AFL-CIO. “So I was sure to respect their timetable.”