Civil rights leader Dolores Huerta has accused Cesar Chavez of sexually assaulting her in the 1960s, saying she was pressured into one encounter and forced into another, as new reporting has detailed broader allegations against the late labour organiser.

Huerta, who co-founded the United Farm Workers union with Chavez, said in a statement that she decided to speak out following a multi-year investigation published Wednesday that outlined a pattern of alleged sexual misconduct.

The report included testimonies from women who said Chavez molested and assaulted them when they were minors.

Huerta said her first sexual encounter with Chavez occurred after she was "manipulated and pressured" and "didn't feel I could say no because he was someone that I admired, my boss and the leader of the movement."

She said the second encounter was forced "against my will, and in an environment where I felt trapped."

"I believed that exposing the truth would hurt the farmworker movement I have spent my entire life fighting for," Huerta, 96, said, explaining her silence. "Cesar's actions do not reflect the values of our community and our movement."

The Chavez family did not dispute the allegations and said it was devastated by the report.

"We wish peace and healing to the survivors and commend their courage to come forward," the family said in a statement, referring to Chavez as "our father."

The accusations have prompted the United Farm Workers to cancel planned celebrations of Chavez, while some cities have cancelled or renamed activities in his honour.