Catherine Frazier, a Maryland state hospital worker, discusses payroll mistakes during a recent meeting in Annapolis with employees from the Department of Health and Mental Hygiene. (Jeff Pittman/AFSCME)

Corrections officers, hospital staff and other Maryland public employees have flooded a state hotline with calls since the government admitted it has shortchanged many workers for overtime, night shifts and special assignments that involve extra pay.

“Our members all have the same big three questions: Who was underpaid, for how long, and when will it be fixed?” said Patrick Moran, president of AFSCME Maryland Council 3, the largest union representing Maryland public employees.

State officials say they still do not know the exact scope of the problem, but they say it could stretch back decades, affecting up to 13,000 current employees and an unknown number of retired and former public workers.

Employees such as Catherine Frazier, a personal-care assistant and AFSCME representative at the state-run Spring Grove Hospital in Catonsville, are frustrated as they wait for answers.

The Maryland State House in Annapolis. (Mark Gail/The Washington Post)

“At one point, I was doing overtime every day,” Frazier said. “Why should we try to work overtime to get extra money if we’re not going to get all of it?”

The Department of Budget and Management discovered the problem while testing a new digital payroll program that the state installed at most agencies after May 25. Previously, the state was using dozens of different payroll systems, many of which were paper-based and required manual calculations that could lead to human error.

By running old timesheet data through the new program, officials realized that the computer numbers did not match the manual calculations from the past. The review looked at compensation for 100 employees from 24 agencies, according to union officials who were briefed on the analysis.

The Department of Budget and Management plans to conduct a new round of tests in coming days to gain a better sense of how many workers have been affected by errors and how much back pay the government might owe. Department officials have offered few specifics about what that work will entail.

Last week, the department estimated that the state underpaid affected personnel by $2 to $30 each pay period. If 13,000 current employees were shortchanged by that amount during each of the state’s 26 pay periods, the total could be anywhere from $676,000 to $10 million for a single year, not counting retired and former personnel.

Union leaders, who received sparse information when they met with agency officials on Tuesday, said the state promised to brief them again in about two weeks.

“We discovered the problem, and we’re committed to fixing it,” said Budget and Management spokesman Eric Shirk. “We’ll keep gathering more information, and there will be more talks with the unions.”

State officials say determining how much each employee is owed could take years, because much of the payroll system was paper-based. Agencies would have to review thousands of old records, some of which they may have already discarded.

“I don’t know how they would accurately figure out what people are owed,” said Heather Hockman, a night-shift nurse at the Western Maryland Hospital Center. “Nobody has given us any answers for that quite yet.”

Another option would be for the state to try to reach a financial settlement with the relevant unions, including AFSCME, AFT-Maryland and the State Law Enforcement Officers Labor Alliance, which would then decide how to distribute the money to members.

The state attorney general’s office said Maryland and federal labor laws would allow such an agreement.

But Jimmy Dulay, president of the law enforcement officers’ union, said there are no easy solutions, even with a possible settlement.

“I can’t sign off and agree to something for an individual person who wants to do their own thing and get exactly what they’re owed,” he said.

AFSCME’s Moran has insisted that the state should determine how much each employee is owed and pay exactly that amount.

For retired employees, past earnings affect how much money they receive from their pension plans, so the state may have to adjust benefits both retroactively and for the future.

The payroll mistakes affected employees who earn more than their basic pay rate for certain work, such as for overtime, late shifts or especially hazardous duties.

Most State Police officers do not have permanent hours, meaning they rotate at some point to late shifts that qualify for extra pay. Others work as bilingual translators or provide field training, which also increases their rates.

“It’s likely to affect the majority of our members,” said Dulay, whose group includes about 1,800 state employees.

Frazier, who has worked a combined 19 years at state hospitals, said she frequently noticed discrepancies between paychecks for periods in which she worked the same late shifts and overtime hours. She said the mistakes can have a big impact on employees in the long run.

“I have co-workers who have worked for the state for 30, 40, even 50 years,” she said. “A lot of the staff at these facilities are single females with children. Doing overtime is what helped them get their kids through college, buy them that extra pair of shoes or send them to camp over the summer.”

Union officials say payroll mistakes have been commonplace for years, but the state never acknowledged a systemic problem until now. Instead, Moran said, individual agencies would fix specific mistakes after being alerted to them, and say they were isolated incidents.

“The system would work great for a few weeks, and then another glitch would occur,” he said. “It was inconsistent, but there was consistently a problem.”

The news payroll system is in place at all agencies except the Department of Public Safety and Correctional Services, which has especially complicated compensation guidelines. That department is scheduled to have the new program fully functioning by August.

Budget and Management officials say the previous errors should not occur with the new system, but some union officials remain skeptical.

“We don’t know whether it’s really fixed,” Moran said. “We’ll see over the next few weeks.”