D.C. Public Schools teachers may have to work without pay if the federal government shutdown continues past the end of the month.

A spokesman for Mayor Vincent C. Gray (D) said that nearly 4,000 teachers and other city workers will be paid on time on Tuesday. But that may be the last on-time payday for a while for the men and women who educate city kids.

The District’s regular funds are frozen because of the federal government shutdown. The city has been using a $144 million contingency reserve fund to pay city employees to stay on the job. But that cash is running out.

It’s “questionable” whether the District will be able to make its next payroll on Oct. 29, said Gray spokesman Pedro Ribeiro. “And after that, all bets are off.”

Gray and other D.C. leaders have been pushing Congress to pass a bill that would allow the District to use its own locally raised dollars to fund city government.

“It’s unfair to ask people to work for free,” Ribeiro said, explaining that teachers will be asked to continue to report to work even if paychecks are delayed. They will receive back pay, but many have bills and mortgages that can’t be put off, Ribeiro said.

D.C. charter schools are also facing a financial pinch if the shutdown continues past Oct. 25, when they are each supposed to receive a substantial payment from the city. That payment — which amounts to a quarter of each school’s annual public funding — will not arrive until the Capitol Hill standoff ends.

In an e-mail sent Sept. 25 — six days before the shutdown began — the executive director of the D.C. Public Charter School Board urged school leaders to begin conserving cash in case of a prolonged shutdown.

“It seems hard to imagine that the government would remain shut down for nearly a month or more,” Scott Pearson wrote, “but anything is possible.”