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.
The free event brings music, the arts, and of course, books, to children along with games, food, and other activities.
Stockton has started the ball rolling to bring a California State University campus to the city.
Stockton has released about a half dozen videos so far, all featuring locals telling their own stories of why "Stockton is Home."
Event organizers in Stockton are looking for at least 1,034 marchers in time for the slew of March For Science events happening in more than 500 cities around the world on Saturday.
An 18-year-old Stockton homicide suspect was arrested Tuesday in Sacramento.