An estimated 1,000 people have shown up at Market Basket supermarket chain headquarters in a show of support for the company's former chief executive.

Employees and others loyal to former CEO Arthur T. Demoulas rallied in Tewksbury on Friday to press for his reinstatement.

The new CEOs said in a letter to workers Thursday that those who walk away from their jobs could be fired.

Demoulas, a member of the family that owns the privately held chain, lost his job last month in a long-running battle with a cousin for control.

The new CEOs said the power to reinstate Demoulas lies with the board that fired him. The board plans a telephone conference Monday to discuss the workers' demand. Employee representatives were invited.

The chain has about 70 stores in Massachusetts, New Hampshire and Maine.

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