"Justice failed us," the victim's brother Jose Luis Vasquez Jimenez said. He joined a dozen supporters who stood silently outside the courtroom holding Maria Isavel's photograph.
The case was the nation's first criminal one involving a heat-related death of a farmworker.
Maria Isavel, 17, was two month pregnant when she died in May 2008. Prosecutors said supervisors denied her shade and water as she pruned grapes in a San Joaquin County vineyard for nine hours in hot weather.
As part of the plea deal, the supervisors, Elias Armenta and his sister Maria Colunga were sentenced to community service, probation and $1,370 in fines.
The plea deals also banned both from ever again working in farm labor contracting.
California introduced the first heat regulations in the nation in 2005 to protect the state's 450,000 seasonal workers, but advocates said the rules were routinely violated.
The Associated Press contributed to this report.