The plaintiffs say the "shelter has a duty to help, not harm, homeless dogs and cats."
The Animal Legal Defense Fund along with three people from Stockton filed the lawsuit against the City of Stockton.
The suit is not asking for money, only that the animal shelter follow the law.
The shelter is required to hold strays for at least 6 days before euthanization.
But Animal Legal Defense Fund Attorney Jenni James says the shelter's records show a different story over a one year period.
"Early euthansias are happening, 1,500 animals were euthanized before the expiration of the Stockton shelter's minimum holding period," says James.
James says 80 percent of the animals are behind locked doors where the public never sees them.
"Only about 20 percent of the animals are truly being given a meaningful chance of adoption," says James.
The City of Stockton is not commenting on the lawsuit.
This week Stockton is playing to host to the $100,000 Men’s Challenger tournament, with some of the top up-and-coming tennis players in the world.
Stockton is mounting a major recruiting drive for its police department. The goal is to hire 50 new officers by the end of June.
Stockton Police are investigating an attack on an eight-year-old boy that was videotaped and posted on social media. The boy was beaten and his bike stolen.
The council voted to buy two adjoining buildings and the purchase will actually save the city money.
Stockton has become the first place in the nation to have a rapid transit bus route that is all electric. The new service starts Wednesday.