People sit on a train as it makes a stop at the Reagan National Airport Metro station. (Matt McClain for The Washington Post)

More than a dozen nonprofit organizations are backing the call for dedicated funding for Metro — and soon — saying that without it, the system risks further deterioration and drastic service cuts.

The 18 groups say they are aligning with the region’s business community to secure a reliable, bondable annual funding stream for Metro, which stands alone among large subway systems in its lack of a significant source of dedicated funding. Business leaders from 21 regional chambers of commerce and employers’ groups issued a plea last week for dedicated funding and a restructuring of the system’s governing board.

Now, the nonprofits are adding their voice to the mix — highlighting the system’s importance to the region and the potential for further service reductions as key considerations in the fight. The groups, including the Coalition for Smarter Growth, the Sierra Club and the League of Women Voters, released a Statement of Principles in March endorsing dedicated funding and calling Metro “crucial for the economic health and sustainability” of the region.

“Going ahead, it’s gonna take both the business community, with their clout, and the nonprofit community, with our membership, to keep this focus on saving Metro and to win the funding the system needs,” said Stewart Schwartz, executive director of the Coalition for Smarter Growth, which is leading the nonprofit groups’ charge.

The nonprofits break from the business groups and some political officials, however, by eschewing immediate calls for an overhaul to the system’s governing board, though they support structural reforms. Schwartz said the Coalition for Smarter Growth is awaiting the release of a fall study by former transportation secretary Ray LaHood, which is expected to include recommendations on the system’s governance.

Metro General Manager Paul J. Wiedefeld has asked for $15.5 billion over 10 years for capital needs — including $500 million in new dedicated funding annually — and concessions from the transit agency’s unions. Wiedefeld also broadly supports the demand that board members have a singular fiduciary duty to the transit system, which business groups and some officials have called for.

Republicans in Virginia have said any increases in funding should be tied to labor and governance reforms.

“The one thing we don’t want to see is we don’t want to see political gridlock over structural and governance issues that end up delaying or endangering the additional funding the system needs,” Schwartz said.

The nonprofits say state and local jurisdictions should prevent Metro from falling into a “death spiral” by providing the funding it needs and ensuring frequent and reliable service. Budget woes, stemming partly from lower-than-expected ridership, forced Metro to raise rail and bus fares and reduce service frequency on five of six lines beginning this week.

Nancy Soreng, co-chair of a Metro working group of the League of Women Voters of the National Capital Area, said it’s up to regional leaders to determine how to reform the system’s governance and labor but that funding can’t wait.

“The most urgent thing for us is to get the three jurisdictions to agree on a dedicated funding source,” she said. As for structural reforms: “That’s a battle that we’re going to stay out of, and we’re going to let the politicians sort that out.”

Soreng was quick to note that the League of Women Voters has endorsed a sales tax for Metro since at least 1980, as the group’s website reflects.

“A sales tax which excludes such necessities as food and medicines would be the best means of financing mass transportation in the metropolitan area,” it points out. A regionwide sales tax, endorsed by a technical panel of the Metropolitan Washington Council of Governments, is among the funding mechanisms regional leaders are weighing. Soreng said her group is open to other means of raising the money if the region can agree on them.

The Coalition for Smarter Growth stopped short of advocating a specific funding mechanism.

“We believe that the jurisdictions should commit to a level of funding and then find the mechanisms that work best for each of them,” Schwartz said.

The nonprofits are calling for dedicated funding to be established by the conclusion of the fiscal year next June.

“Waiting any longer means that capital costs could rise, you could fall further behind in the capital restoration in the system,” Schwartz said. “The operating gap could increase further, and there could be more service cuts.”