U.S. Reps. Chris Van Hollen and Donna Edwards debate in Silver Spring on April 15. They are in a hotly contested race for the Democratic nomination for U.S. Senate. (Tomás Guevara/Para El Tiempo Latino)

A labor union that was instrumental in electing Rep. Donna Edwards (D-Md.) to the House is now trying to keep her out of the Senate.

The Service Employees International Union spent more than $1 million supporting Edwards in 2008, helping her topple the incumbent, Rep. Albert R. Wynn, in the Democratic primary. About a quarter of that money came from SEIU 1199, a Baltimore affiliate representing health-care workers.

Now, Committee for Maryland’s Progress, a super PAC largely funded by 1199, has spent close to $500,000 to try to defeat Edwards in her neck-and-neck primary for the Senate against Rep. Chris Van Hollen. The seat is being vacated by Sen. Barbara A. Mikulski (D), who is retiring after five terms.

“We’re disappointed that, instead of the fight for a $15 [minimum] wage, SEIU 1199 is spending their hard-earned member money to defeat a woman their own organization rates as 100 percent on the issues that matter to working families,” Edwards spokesman Benjamin Gerdes said in a statement.

Pat Lippold, the local’s vice president for political action, said the significant turn was driven by Edwards not defending a unionized hospital in Laurel when a non-unionized hospital made plans to open nearby. The union wanted help securing federal funding for a university-run medical system to take over the struggling Laurel Regional Hospital. Instead, Edwards wrote a letter supporting the new hospital. The formerly full-service Laurel hospital is being downsized to an ­ambulatory-care facility.

“This isn’t quid pro quo,” Lippold said.“We had very high hopes for her. We tried and made several efforts to make her successful. At the end, she doesn’t move the needle.”

Union members also complained that Edwards’s office was not helpful with Social Security issues and other constituent concerns, Lippold said.

“We were making the case that she needed to build relationships and spend more time in the district,” Lippold said.

Other local unions have endorsed Edwards.

“Whenever we’ve called on her to be there, she’s always been a phone call away for us,” said Mike Wilson of Local 400 of the United Food and Commercial Workers, which represents mostly workers in the food industry.

Several people involved in the local labor movement said there also has been a personality clash between Edwards and the leaders of 1199 who assumed office after her first election.

After helping her win the 2008 primary, the union expected a closer relationship with Edwards than materialized, said several people involved with the union at the time.

A senior official in Edwards’s office said the union asked the lawmaker to hire an SEIU member as a full-time staff person. Lippold denied that claim.

“A lot of the Maryland political establishment [were angry] at 1199 for going against an incumbent,” said one former staff member for the union who spoke on the condition of anonymity to discuss internal issues. “Most people at 1199 didn’t think they got out of her what they thought they would.”

Union leaders were particularly upset, the staff member said, that Edwards was overheard saying at events that she wasn’t beholden to anyone — including SEIU.

There’s also a desire to earn credit with leaders in the General Assembly who are supporting Van Hollen, particularly the more conservative state Senate.

“They believe this is a longer-term play,” said one local labor activist.

The union local did not endorse Edwards in 2014, a snub that went unnoticed in her easy reelection campaign.

Now the group is making a splash.

A television ad run by the super PAC describes Edwards as ineffective. Mailers sent by the group say that “seniors can’t trust Donna Edwards” to protect Social Security and Medicare because during 2011 debt-reduction negotiations, she told the Fox News Channel that “everything has to be on the table.”

Van Hollen’s campaign has used the same quote to argue that he and Edwards were in agreement at the time, a rebuttal to claims by Edwards that Van Hollen was ready to cut entitlements during those negotiations.

Another mailer, designed to look like a newspaper called the Maryland Progress Report, says that “those who know Rep. Edwards refuse to support her for Senate.”

About half of the $600,000 raised by the super PAC by early April came from 1199. SEIU Local 32BJ, which represents property service workers, contributed $15,000 to be used only for canvassing.

The rest of the group’s money comes largely from donors who have already given the maximum possible to Van Hollen’s campaign. One notable contributor is Haim Saban, a billionaire Israeli American entertainment mogul who gave $100,000. Saban is also a major supporter of Hillary Clinton.

Other SEIU locals that have endorsed Van Hollen chose not to get involved in the super PAC.

“We’ve decided that we’re not going to be a part of” the independent effort, said Terry Cavanagh of the SEIU Maryland/DC State Council.

“We have nothing to do with it,” a spokesman for SEIU Local 500 said.

The national SEIU has not weighed in on the Senate race. Its political action committee donated $20,000 to a pro-Edwards super PAC run by the Democratic women’s group Emily’s List before the local endorsements occurred, and $5,000 to Van Hollen’s campaign after. SEIU said the money it gave to Women Vote! was for joint voter research, not to help Edwards’s campaign.