ENCINITAS, Calif. (AP) -- Administrators of a California school district say they are being cautious as they launch what is believed to be the country's most comprehensive yoga program for a public school system.

The Encinitas Union School District starting in January will offer yoga instruction at all of its nine schools despite a protest by a group of parents who say they are prepared to sue to halt the program.

Opponents say they believe the yoga classes will indoctrinate their children in Eastern religion.

School officials say there will be no chanting, prayer positions or cultural references that would raise concerns.

The question over whether yoga is a religious practice or simply exercise is one that public schools are increasingly facing with its growing popularity as a way to ease student stress.