One of the world's best-known wine makers has been hit by complaints that it forced workers to quit the United Farm
Workers (UFW) trade union.
Gallo insists its labour practices are sound
California's Agricultural Labor Relations Board filed an action against Gallo of Sonoma, an offshoot of the Gallo family, the world's biggest wine makers.
The complaint will at least delay the elimination of union labour at the wine producer, whose workers recently voted on a proposal to decertify the UFW.
The Board argues that vineyard staff - many of whom are migrant workers with limited language skills - were duped into supporting the decertification.
Their ballots remain locked in a vault, and cannot be scrutinised until the charges against Gallo can be resolved.
According to the Board, a foreman at the winery encouraged employees to support a petition to decertify the UFW.
The initiative to decertify, therefore, allegedly came from vineyard management, and not from the workers, as labour laws dictate.
"The effort was totally orchestrated by Gallo management," said Marc Grossman, a spokesman for the UFW.
"It was patently illegal.".
Gallo denied the charges, and pointed out that other allegations against the company had already been dropped.
The dispute is the latest step in a long series of struggles to unionise agricultural workers in California.
Gallo workers voted for union representation in 1994, but were not able to reach an agreement with the company on contract terms until 2000.
Even then, many complained that they did not win the sort of benefits packages enjoyed by unionised workers in other industries.
In the farming sector, especially in the southern states of the US, employers depend on migrant workers, many of whom are on short-term or informal contracts.