BIDDEFORD — Behind the deli counter at Market Basket in Biddeford, clerk Jeremy Webster has nothing left to sell, and no customers to buy it if he did.

So he cleans. And cleans.

“We’re cleaning about 20 times a day,” said Webster, who has been a Market Basket employee for 19 years. “We’re still working.”

The Biddeford store was virtually empty Thursday, with just a handful of customers and employees inside. Only one cash register was open, and nobody was in line.

Outside, it was a different story. Dozens of off-duty employees held protest signs in the otherwise empty parking lot and on Alfred Street by the entrance to the shopping center. What they want is to have their beloved, recently ousted CEO, Arthur T. Demoulas, reinstated.

Market Basket workers in Biddeford vowed not to back down in the face of an ultimatum issued Wednesday by the company’s new co-CEOs: Get back to work by Monday, or you’re fired.

“I’ll go down with the ship,” said bagger Travis Phillips, holding a sign that said, “We are Market Basket. Save ATD (Demoulas). Bring our boss back.”

On Alfred Street, about a dozen employees held up signs while passing drivers honked and waved in support. Meanwhile, two camera crews and one newspaper reporter vied for the workers’ time and attention.

Heidi Kleiner, a 20-year employee who works as the Biddeford store’s receiver, has few goods to take in because most of Market Basket’s delivery drivers also are refusing to work. So she was out protesting to save what she believes is the integrity of the company.

“The pressure keeps on mounting, with a full-page ad looking to replace store directors, some of whom have worked here for 30 years,” Kleiner said.

Those ads, and a scheduled job fair to hire replacement workers, do not faze the Market Basket employees in Biddeford, said store director Micum McIntire.

“They’re all on board,” he said. “We’re going to continue to fight.”

Customers have shown their solidarity by boycotting the store until the workers’ demands are met, McIntire said. A sign in the front window reads, “Help us. Boycott us.”

The lack of new shipments of fresh meat and produce is not really an issue anymore, he said, because there are no customers left to buy them anyway. The store was only one-quarter staffed on Thursday, and most employees appeared to have little to do.

But that’s the way McIntire wants it.

“We want him (Demoulas) back in place,” he said. “There’s no going back.”

Market Basket’s owner, Massachusetts-based Demoulas Market Basket Supermarkets Inc., has 70 stores in Massachusetts and New Hampshire, and one in Maine. It opened the Biddeford location last August. About 25,000 employees worked for the company before the protests began.

Managers and assistant managers at 68 of the 71 New England stores have signed petitions vowing to resign if Demoulas isn’t restored with full authority. Employees have been holding daily demonstrations, the largest of them in front of Market Basket’s corporate headquarters in Tewksbury, where hundreds of workers have held up signs and shouted in protest.

At issue is the June 22 ouster of longtime CEO Demoulas by the company’s board of directors. Demoulas is a hero to many in the company because of his employee-friendly demeanor and generous compensation policies.

The leadership coup was engineered by Demoulas’ cousin, Arthur S. Demoulas, and is the result of a decades-old feud between the two.

Recently, the two part-owners clashed over the company’s future business strategy. Arthur T. wanted to use its cash reserves to open more stores, while Arthur S. insisted that the money be paid out in dividends to the family-owned company’s shareholders. The dispute ended up in court, where Arthur S. won a judgment to distribute $300 million to the shareholders.

The mass protests and walkouts began roughly two weeks after Arthur T. was fired. Since then, the employee revolt has steadily gained momentum, with longtime customers joining the fight by participating in demonstrations and refusing to shop at Market Basket.

On Thursday, Denise Walsh, a longtime Market Basket shopper in North Billerica, Massachusetts, started a fundraising campaign on gofundme.com to purchase advertisements in local newspapers encouraging readers to join in the boycott. Within four hours, the campaign had raised more than $9,000 from nearly 400 contributors.

Competing grocery store chains such as Hannaford and Shaw’s have benefited tremendously from the boycotts, officials at those companies have said.

Scarborough-based Hannaford Bros. Co. supermarkets said last week that it was moving some of its workers from Maine to New Hampshire to help with staffing, where 30 Market Basket stores compete against 34 Hannaford stores. In some cases, the Maine workers are being put up in hotels, they said.

The Market Basket board is considering an offer from the former CEO, and others, to buy the company, and a decision is expected soon.

Webster, the deli clerk, said he and his fellow workers are trying to remain optimistic that, one way or another, Arthur T. Demoulas will be reinstated as CEO.

“Hopefully it goes our way,” he said.