The Labor College grounds and buildings. (Jeffrey MacMillan/Jeffrey MacMillan)

The National Labor College, an education venture for working adults supported by the AFL-CIO, will close next year because of financial difficulties school officials attribute in part to the construction of a conference center several years ago on the Silver Spring campus.

The college, with 599 online students this fall, announced Wednesday that its board of trustees voted this week to accept a closure plan. Word of the impending shutdown had been circulating since at least mid-November.

“We’re all very, very sad,” said Paula E. Peinovich, the college’s president. The college will offer courses through the spring semester and have its final commencement in April — 17 years after it became an independent, degree-granting institution.

Peinovich said the college was burdened by debt incurred in a major campus renovation that began in 2003, including the construction of a 72,000-square-foot conference center named for Lane Kirkland, the late AFL-CIO president. The center, dedicated in 2007, was unable to generate enough revenue to erase the debt, Peinovich said, and even failed to cover its own operating costs.

Peinovich said the college owed about $30 million when she took over as president in 2010.

“A lot of the challenges go back to the decision to build the Kirkland Center,” said Bob Bruno, a trustee of the college who is a professor of labor and employment relations at the University of Illinois. “This overhang of debt that was carried forward just became something [the college] couldn’t get out of.”

Alumni and students expressed distress. “I think it is a crying shame that the only specialized labor college in the United States of America cannot support itself to continue,” one alumnus wrote on the college’s Web site. “This institution represents a lot more than labor students represented by labor unions. It represents a way of life in America.”

The college traces its history to a labor studies center that AFL-CIO leaders founded in 1969. In the early 1970s, the center moved to a 47-acre campus on New Hampshire Avenue. It grew into a larger academic enterprise, first in partnership with Antioch College and then as an accredited institution in its own right.

The college specializes in labor studies, seeking to help union members and their relatives get bachelor’s degrees. In recent years, it launched a school of professional studies with bachelor’s programs in construction management, business administration, and emergency readiness and response management.

All of its students, Peinovich said, study part time and online. Tuition is $297 per credit hour for members of AFL-CIO unions and their relatives.

The college employs 58 faculty and staff members and has an annual operating budget of $12 million, she said, with about $5 million funded by the AFL-CIO. Richard Trumka, president of the AFL-CIO, is chairman of the college’s board of trustees.

Thea Lee, deputy chief of staff for the national labor organization, blamed the closure on “financial difficulties that became insurmountable at some point.”

The Kirkland Center was built while John J. Sweeney was head of the AFL-CIO. But Lee said Trumka did not want to “sit and point fingers” about a project that labor leaders once viewed with optimism.

Peinovich said the board vote Monday to accept the closure plan was unanimous.

Under the plan, the college’s final commencement will be April 26, with about 100 to 150 students expected to receive bachelor’s degrees. The college is seeking to help remaining students finish their degrees in partnership with other schools. Trustees have approved a letter of intent to sell the 47-acre campus to Monument Realty. A sale price has not been announced, but proceeds will help cover the college’s debts.

The venue for the last graduation will be the Kirkland Center.