One of the country’s most powerful union organizations is staying out of Maryland’s competitive Democratic Senate primary.

The Maryland State and District of Columbia AFL-CIO has decided not to endorse a candidate to replace Sen. Barbara A. Mikulski (D), president Fred Douglas Mason Jr. confirmed Tuesday.

Mason said a committee of several dozen executive board members and representatives from the state’s five central labor councils interviewed U.S. Reps. Donna F. Edwards and Chris Van Hollen, both Democrats, as well as Republican Richard Douglas. To win support, a candidate would need the backing of two-thirds of the committee members. None of the three cleared that bar.

“It happens sometimes when there are two very good candidates,” Mason said of Edwards and Van Hollen. “They’re both good quality candidates, they’ve both represented Maryland [well] in their respective positions. . . . That’s why it was so hard.”

The answers that the two Democrats gave in 19-page questionnaires and 1 1/2 -hour-long interviews were “very similar,” Mason said.

Both have strong ties to labor, although Edwards in particular rose to political power with the support of organized labor. She has a 99 percent lifetime score from the organization; Van Hollen ranks at 95 percent.

However, Edwards angered the AFL-CIO in 2012 by endorsing now-Rep. John Delaney (D) in a primary in which Maryland labor groups were backing his opponent.

“This action on her part will certainly be considered in our future relationships,” Mason wrote at the time.

Edwards, more than Van Hollen, needs support from outside groups, because he has amassed far more campaign cash than she has. Van Hollen has more than $4 million in the bank; Edwards has $368,000. National progressive groups have lined up behind her campaign, but local unions have split. On Monday, the statewide and Baltimore firefighters’ unions backed Van Hollen.

However, polls find that Edwards has the early lead over Van Hollen, whom she has aggressively attacked as a political insider.

A national AFL-CIO spokesman said the lack of a state endorsement means the country-wide organization will not get involved in the primary. However, local AFL-CIO chapters in Maryland are free to endorse a candidate.

In 2014’s gubernatorial primary, the state AFL-CIO endorsed then-Lt. Gov. Anthony G. Brown (D) over two rivals; he went on to win the primary, but lost the general election to Republican Larry Hogan.