Dunnewood Vineyards, a Ukiah winery owned by Constellation Brands, is being sued by the U.S. Equal Employment Opportunities Commission over accusations that it tolerated discrimination against Mexican-born workers.

The EEOC lawsuit, filed Wednesday in the U.S. District Court, alleges that a Dunnewood supervisor regularly harassed winery worker Julio Perez-Lombera and other Mexican-born workers, using racial slurs on a daily basis and telling them to go back to Mexico.

The supervisor had allegedly subjected Perez-Lombera and other Mexican-born employees to derogatory comments about their national origin since 2004, calling them "wetbacks," "dumb beaners" and "black beanies," according to the complaint.

Although the supervisor was also Latino, he was born in the United States while the workers he allegedly harassed were born in Mexico, the EEOC said. The supervisor was not identified in the lawsuit.

"It's hard to understand why a member of one group would harass members of the same group on the basis of their national origin, but, sadly, there's all kinds of discrimination in too many workplaces," said Michael Baldonado, San Francisco district director for the EEOC.

Perez-Lombera was hired as a racker/blender at the winery in 2004, the lawsuit said. After he complained, the harassment escalated, and Perez-Lombera was assigned to a less desirable shift and eventually terminated, according to the suit.

"The egregiousness of the harassment, I think, is particularly striking in this case," said Raymond Cheung, senior trial attorney for the EEOC. "The harassing comments were made at the factory in plain sight. Other people heard it, coworkers heard it, upper management heard it ... and they turned a blind eye to it."

A winery worker in Ukiah referred phone calls to Constellation for comment.

"Constellation Brands is an equal opportunity employer and takes this responsibility very seriously," said Cheryl Gossin, Constellation's vice president for corporate communications, in an email. "We have not yet been formally served with the lawsuit, and as policy we do not comment on pending litigation."

Cheung said at least two other employees besides Perez-Lombera were harassed, and the supervisor seemed to pick on the employees who spoke the least amount of English.

Because the alleged harasser was a manager, he was acting as a proxy for Constellation and the company is liable for his actions, Cheung said. If the harasser was not a manager, then federal attorneys would have to prove the company was aware of the actions — a higher hurdle to clear in discrimination cases.

The EEOC enforces federal laws that make it illegal to discriminate against a job applicant or an employee because of the person's race, color, religion, gender, national origin, age, disability or genetic information.

For the first time ever, the EEOC last year received more complaints about retaliation against employees who reported problems than complaints of racial discrimination.

The lawsuit was filed after the EEOC failed to reach a settlement in negotiations with the company. Last year, it filed eight employment discrimination lawsuits in Northern California and 271 lawsuits nationwide.

Constellation, which owns brands like Clos du Bois and Robert Mondavi, is the world's second-largest wine company behind E&J Gallo. The company employs 4,300 people in 125 countries, according to its website.