Minnie Allen has worked in the Library of Congress’ cafeteria for 25 years, arriving each day at about 5 a.m. and opening up the cafeteria early as she waited for her shift to begin at 6.

But in recent days, Allen — who is known as “Miss Minnie” — has been unable to get out of the cold and into the Madison Building when she arrives, often in the dark.

Her staff identification badge, officials say, doesn’t allow her access until a time closer to her shift. So instead, Allen, who is about 70, sits on a chair in a door’s entryway, courtesy of the kindness of a few police officers.

The situation has angered Library union officials, who say Allen is a longtime employee who should be allowed to enter the cafeteria when her bus drops her off to work.

The cafeteria’s vendor, on the other hand, maintains that Allen was never authorized to have a key to the cafeteria. And the decision to not let her into the building, they say, is one made by Library officials.

“Miss Minnie has a contractor badge, which restricts access” to certain hours, said Charles Healey, vice president of I.L. Creations, which runs the cafeteria. “We have no control over the security restriction.”

The dispute is the latest in the rocky relationship between I.L. Creations and the cafeteria’s union, UNITE HERE Local 25.

Since I.L. Creations took over about 10 months ago, the two organizations have fought over pay, benefits and job security.

Healey said the latest disagreement began a couple of months ago, when management discovered that small amounts of candy bars and sodas occasionally went missing.

Officials soon learned that some employees had unauthorized keys and were showing up during hours when the cafeteria was closed. So they told the Library, which in turn reminded its officers about the access restrictions of contracted employees.

Allen, meanwhile, had for years been getting to work early and showing up before the cafeteria opened. She also had a key to the cafeteria itself, which I.L. Creations asked that she return.

The investigation of the missing candy and soda had “opened up a can of worms,” said Healey, and raised the question of whether Allen should be able to continue to let herself into the cafeteria.

“I really thought it was a safety issue more than anything else,” he said. “God forbid there was a fire, and no one knew she was there.”

But the union isn’t convinced. John Boardman, the chapter’s international vice president, declined to discuss the details of the case. But, he said, the union is “actively pursuing” the issue.

“We are outraged by the treatment of this 25-year worker,” he said.

Other Library unions have joined in. In a letter sent to the Library’s unions, the president of the LOC Professional Guild asked employees to circulate Allen’s story.

“The latest outrage is just too much for words,” wrote Saul Schniderman, who heads the Guild even though it technically doesn’t include the cafeteria workers. “For as long as anybody can remember Miss Minnie arrives — by bus or being driven by a neighbor — to the Library of Congress at 5:00 a.m. and ‘starts up’ the cafeteria by turning on lights, cooking stations, etc.”

He added: “Miss Minnie — who can remember the days when her union picketed Peoples drug store over their segregated lunch counters — deserves our support.”

Allen’s situation comes amid troubled times for the cafeteria. At the end of October, I.L. Creations fired about half a dozen of the 30-some employees who work at the cafeteria.

Of the four people in Allen’s classification, she was the only one who wasn’t fired, Healey said.

He attributed the layoffs to four months of “significant losses” and said the employees will be called back if sales pick up. But he also said I.L. Creations has a different business model than previous vendors — one that in other cafeterias the company runs requires as few as 12 employees.

“We have a completely different business model with a different menu and a different system,” he said, “but we have the same employees and the same union.”