A partial government shutdown could result in double pay for hundreds of thousands of federal workers if Congress and President Trump don’t quickly agree to a spending package.

Federal funding runs out midnight Friday and a General Services Administration pay period ends the next day, meaning a shutdown lasting even one day — through Saturday — could trigger penalties under a Great Depression-era law.

If employees aren’t paid on time, the Fair Labor Standards Act allows "liquidated damages" that could double a worker's pay.

Attorney Heidi Burakiewicz, who sued on behalf of about 25,000 people paid late because of the last shutdown in 2013, said employees deemed “essential” who work Saturday would be entitled to damages, even for a one-day spending lapse, if they work overtime or if non-payment drops their overall pay below minimum wage.

“The people who are ‘essential’ are often the people working weekends,” she told the Washington Examiner. “I’m concerned that the powers that be that are contemplating whether another shutdown should happen are not thinking about the consequences that hardworking federal employees are going to have to deal with.”

The number of people affected may be greater than during the 16-day 2013 shutdown, especially if a funding lapse lasts for a full 14-day pay period. Unlike in 2013, Congress has not pre-emptively funded paychecks for members of the military and civilians who work for the Defense Department. Legislation protecting military workers in 2013 reduced the number of “essential” workers not paid on time from more than 1 million to a few hundred thousand.

Trump has warned about the effect of a partial shutdown on the military, but Democrats seeking a deal protecting young illegal immigrants could derail a spending proposal pending before the House of Representatives. Many Senate Democrats object to that bill, which does not include an immigration deal, as do at least two Senate Republicans, potentially making it impossible to find 60 votes to proceed.

The GSA referred questions about contingency planning to the White House Office of Management and Budget, a spokesman for which did not respond to requests for comment on Burakiewicz’s interpretation of the federal pay calendar.

“There were so many heartbreaking stories as a result of the last shutdown,” said Burakiewicz, an attorney at the firm Kalijarvi, Chuzi, Newman & Fitch, P.C.

Although federal workers were paid back wages when the 2013 funding lapse ended, she said the delay caused hardship on lower-income people such as federal Bureau of Prisons employees who had to pay bills and expenses for long commutes to distant and dangerous jobs.

One family, she recalled, had a disabled child, resulting in just one adult working so the other could provide full-time care. A delayed paycheck meant decisions about prioritizing bills. Other families incurred unwanted credit card interest, she said.

In February, U.S. Court of Federal Claims Judge Patricia Campbell-Smith ruled in favor of Burakiewicz’s clients, finding the FLSA applied even though a separate law, the Anti-Deficiency Act, seemed to prevent the government from issuing on-time pay for work performed Oct. 1-5, 2013, at the start of the 16-day shutdown, because those funds weren't approved by Congress.

Any payout for workers affected by a 2017 shutdown would likely come years later.

Despite a legal win nearly a year ago, experts are still working to calculate damages for workers paid late in 2013. The calculations are time-consuming, requiring information from many agencies. Workers who earned overtime are entitled to be paid that amount for a second time, but damages for work up to a standard 40-hour week are pegged to the minimum wage.