Helen Chavez, the widow of the civil rights and farm labor leader Cesar Chavez, died on Monday in Bakersfield, Calif. She was 88.

Her family announced her death in a statement released through the United Farm Workers, the union her husband founded. No cause was given.

Though Ms. Chavez preferred to be out of the spotlight, she was active in the union, serving as its bookkeeper and the head of its credit union. She was arrested in 1978 for demonstrating at a farm where the Teamsters represented workers picking cantaloupes.

President Obama issued a statement on Tuesday calling Ms. Chavez “a force of quiet strength” who “left a legacy that will echo for generations.’’