BART virtually emptied out on Tuesday, with 85% fewer riders than it had on an average weekday in February. Combined losses from fares and parking revenue will cost BART some $37 million a month, agency managers predicted.

But the rail agency won’t cut service, even as the coronavirus grips the Bay Area and shelter-in-place orders oblige commuters to stay home.

The reason: BART cannot furlough workers without a 60-day notice, an agency spokeswoman told The Chronicle on Tuesday. It’s bound by labor contracts that keep the agency running a full schedule of 10-car trains — with or without people on them.

“We could cut service, but we still have to pay the employees,” spokeswoman Alicia Trost said in an interview. The agency has not given its workers a 60-day notice for a furlough, she added. That’s partly because officials don’t know what the pandemic will look like in 60 days. It’s also because BART supports its employees, Trost said, and it’s an essential service for people who still have to show up to work, get to medical appointments or make other vital trips.

Notably, BART has to provide enough space for passengers to maintain social distancing — hence the sparse, 10-car trains.

Last week Board President Lateefah Simon sent letters to House Speaker Pelosi, U.S. senators Dianne Feinstein and Kamala Harris, and several state and local leaders, asking for emergency stimulus funding to save BART from what she said is a financial crisis. The letters cited an $8.3 billion federal package for coronavirus response efforts, which set $950 million aside for state and local agencies.

“This level of catastrophic revenue loss is not sustainable and threatens future service, Simon said in a statement. “We need reassurance from all levels of government that transit will not be left out.”

Simon’s letters note that BART “examined methods to reduce expenses, but the reality is most BART operating expenses are directly related to labor costs.” Officials found they had limited options to reduce those costs, the letters said, particularly with demands for more cleanings and hand sanitizer in the wake of the pandemic.

“Furloughing workers — I’m not thinking about that right now,” Simon told The Chronicle on Tuesday night. “Our goal needs to be getting on the phone and organizing our elected delegations across the state and the country.”

Board Director Rebecca Saltzman had already circulated a petition earlier that day on Twitter, urging the state to prioritize emergency funding for public transit.

Yet board members have also heard criticism from constituents who wonder why BART is running at full capacity with so few riders.

“It’s a valid question,” Director Debora Allen said. “If your revenue is plummeting you have to think about how to cut costs.”

Other transit agencies have made significant cuts. Caltrain suspended its weekday baby bullet service. The Peninsula rail system saw a 75% drop in day pass and one-way ticket sales during the pandemic. The Golden Gate Bridge Highway and Transportation District reduced ferry service and stopped running bus lines that weren’t picking up many passengers. The cuts didn’t require any staff reductions, said district spokesman Paolo Cosulich-Schwartz.

Muni replaced its cable cars and streetcars with bus shuttles, but San Francisco transportation chief Jeffrey Tumlin said that measure was solely to protect the cable car operators, who don’t have a separated cab. The agency is losing an estimated $1 million a week from rider drop-off.

Gena Alexander, president of Amalgamated Transit Union Local 1555 — the union that represents BART stations agents, train operators, foreworkers and clerical workers — said she has not discussed the possibility of a furlough with agency management.

“We as a union are trying to prepare for whatever may come,” Alexander said. “It’s mapped out in our contract that if there is a bonafide emergency, there’s a way in which they need to do that.”

Rachel Swan is a San Francisco Chronicle staff writer. Email: rswan@sfchronicle.com Twitter: @rachelswan