When Duchy Trachtenberg lost her at-large seat on the Montgomery County Council in 2010, labor groups gleefully took credit.

Elected with labor support in 2006, she was branded a turncoat for pushing to cut cost-of-living increases during the recession and co-sponsoring legislation that restricted police officers’ eligibility for full disability retirement, among other actions. Outraged public-employee unions put her face on a “wanted” poster.

Four years later, Trachtenberg’s bid to return to the council by unseating District 1 incumbent Roger Berliner (D-Potomac-Bethesda) has been endorsed by the Metropolitan Washington Council AFL-CIO and the Fraternal Order of Police Lodge 35. On Monday, she won the backing of the Municipal & County Government Employees Organization, the county union representing about 8,000 non-uniformed workers (the union’s former executive director, Bob Stewart, is managing Trachtenberg’s campaign).

Trachtenberg’s reconciliation with labor supports the idea that in politics there are no permanent alliances or estrangements, only permanent interests.

Labor’s decision to back her illustrates the lengths to which unions are prepared to go to exact payback from council incumbents, and County Executive Isiah Leggett, in the June 24 Democratic primary.

“In all families there are disagreements, and it doesn’t mean that at the end of the day you don’t get back together on the same page,” Trachtenberg, a family therapist, said. “The past is the past. Obviously they placed their trust in me.”

Unions are furious at the council’s decision to eliminate a law that allowed the Fraternal Order of Police (FOP) to bargain over matters that went beyond wages, benefits and working conditions. The change was approved by Montgomery voters in 2012 after a county campaign to support it that relied on public dollars and employee time. This month, a Circuit Court judge ruled that Leggett violated Maryland election law by campaigning for the passage of the ballot measure, known as Proposition B.

Labor groups also are angry over council passage of a bill that requires arbitrators — neutral third parties used to resolve contract negotiations that have reached impasse — to consider the county’s financial condition before ruling.

“Montgomery County is supposed to be a progressive county. Democrats expect us to work for them and be there for them, and you look up and they’re acting like Republicans,” said Metro Council AFL-CIO President Joslyn Williams. The labor group’s 20-member executive board includes representatives of public- and private-sector unions with about 32,000 members who live in Montgomery.

In 2010, the AFL-CIO backed Leggett for a second term and also endorsed five council members (Berliner, Valerie Ervin, Marc Elrich, Nancy Floreen and George Leventhal). Ervin resigned in January, and the AFL-CIO has not endorsed any of the remaining incumbents this campaign season.

Instead, the labor group so far is backing only Trachtenberg and two contenders for open seats: Del. Tom Hucker in District 5 (Silver Spring) and Gaithersburg City Council member Ryan Spiegel in District 3 (Rockville-Gaithersburg).

It is a stark contrast to Prince George’s County, where only one incumbent running for reelection has lost the AFL-CIO endorsement. Williams said the Prince George’s County Council has been more collaborative on labor matters.

The FOP’s slate is also incumbent-free. It lists Trachtenberg, Hucker, Spiegel, at-large challenger Beth Daly and former county executive Doug Duncan, who is challenging Leggett for the Democratic nomination.

“As a labor leader, I don’t know how you support people who have violated every fundamental principle that I am elected and sworn to uphold,” said Gino Renne, president of MCGEO, which on Monday announced that it was endorsing Trachtenberg, Hucker and two other non-incumbents, Ryan Spiegel in District 3 and at-large challenger Daly. The group did endorse one incumbent, at-large council member Elrich, who is considered the most labor-friendly of the group.

Unions have not completed the endorsement process, but leaders say it is unlikely that many incumbents will be added to labor slates. Union endorsements can be important for candidates, especially in Democratic jurisdictions, because they come with money and boots-on-the ground support for candidates in the form of canvassing, phone banks and an Election Day presence around polls.

Montgomery incumbents say their candidate interviews with unions have been turbulent. “Rough and stressful,” said council member Leventhal (D-At Large). “They are conveying that they feel betrayed and disappointed.”

Incumbents have tried to defend their records by arguing that difficult steps taken during the recession, including furloughs, wage freezes and elimination of thousands of positions, have made it possible to award substantial raises in the most recent round of contracts.

“There’s not a lot of recognition of the benefits of the tough choices we made,” said Riemer.

Not all unions are interested in revenge. Service Employees International Union Local 500, which represents maintenance and cafeteria workers and other support staff in Montgomery public schools, has essentially reprised its 2010 endorsements,backing all returning incumbents except Leventhal.

The powerful Montgomery County Education Association, which represents public-school teachers, will meet this week to decide whom to endorse in the county executive race. The teachers union seems likely to endorse Leggett, in light of his proposal to fund the school system at $25 million over the state-mandated minimum in the 2015 budget.

The group will defer its council endorsements until May 21, which happens to be the eve of the council’s final action on the budget. It’s a good bet that members who push for the $25 million — or more — will find their names on the coveted Apple Ballot.