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.
A project to transform the heart of downtown Stockton from blighted buildings and empty lots into a thriving urban center with new housing, shops and restaurants could be moving forward later this month.
After getting some social media heat from activist Erin Brockovich Stockton Mayor Anthony Silva called a town-hall meeting to discuss the recent addition of chloramines into the water treatment process.
Stockton might be a good destination for the next few days for those who consider themselves to be "foodies." Stockton Restaurant Week begins Friday. It's a chance to explore new menus and new venues at bargain prices.
The City of Stockton will be changing part of its drinking water disinfection process by the end of the month.
In Stockton, one of the busiest nights of the year for guns illegally fired into the air is at midnight on New Year's Eve. Celebratory gunfire can result in death or injury.