One of Maryland's most powerful labor unions plans to sit out the state's two competitive congressional primaries, raising questions about its ability to influence the winner of the high-profile contests.

Officials with the Maryland State and D.C. AFL-CIO, which represents about 350,000 workers in more than 500 local unions in the region, said it would make no recommendation in the 4th and 8th Congressional Districts — two open seats that have drawn many candidates and much attention this year.

The union had announced in October that it would not engage in the Senate race to replace retiring Democratic Sen. Barbara A. Mikulski.

The leading Democrats in that contest, Reps. Donna F. Edwards of Prince George's County and Chris Van Hollen of Montgomery County, represent the 4th and 8th Districts, respectively.

Fred D. Mason Jr., the president of the union, dismissed the notion that by not backing a candidate in the state's hottest primary contests it might face a more difficult task in working with the winner.

Both seats are considered safe for Democrats in the general election, so it is the April 26 primary that has drawn the most attention.

“We were friends and supporters before folks decided to run for office,” Mason said. “I fully expect that they will respect our position and that we will be friends afterward.”

He noted that AFL-CIO locals are free to endorse if they choose.

It is difficult to predict who will emerge with the nomination in either district. The 4th District, which covers portions of Prince George's and Anne Arundel counties, has been a generally sleepy contest, even though it includes some well-known candidates, including former Lt. Gov. Anthony G. Brown, former Prince George's County State's Attorney Glenn F. Ivey and Del. Joseline Pena-Melnyk.

The 8th District, which includes parts of Montgomery, Frederick and Carroll counties, is even harder to handicap, with three state lawmakers, a former television anchor who has raised a significant amount of money and a self-funded businessman who has spent millions of dollars on his campaign.

The uncertainty makes an endorsement risky, and it could mean bruising relationships with state lawmakers turned candidates who, even if they do not win a seat in Congress, still wield power in the General Assembly.

“It doesn't really make any difference to them who wins because all of the candidates can be counted on to be pro-labor,” said Matthew Crenson, emeritus professor of political science at the Johns Hopkins University. “Why should they bother to spend their money?”

The AFL-CIO did endorse all of the incumbent Democratic members of Congress in Maryland's delegation save one: Rep. John Delaney of Potomac.

The 6th District lawmaker, who won his first race in 2012 without help from the Democratic establishment, has had a strained relationship with labor.

john.fritze@baltsun.com