A labor dispute at the Pilgrim nuclear power plant in Plymouth has boiled over with management locking out unionized workers and both sides accusing the other of compromising public safety.

The president of the Utility Workers Union of America Local 369 said Wednesday that plant owner Entergy locked out unionized employees after contract negotiations ended Tuesday. The union represents about 90 percent of the plant’s work force.

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President Dan Hurley called the move ‘‘deeply alarming.’’ He called it ‘‘despicable’’ that management continues ‘‘shortchanging’’ employees a week after getting a 20-year license renewal. He says Louisiana-based Entergy is demanding ‘‘major concessions on health care, salary and staffing.’’

Entergy said the plant has implemented an emergency staffing plan because the union reserved the right to walk off the job at any time.