Online reviews can make or break a business, and small businesses are especially vulnerable. Paranoia has driven some businesses around the country to sneak non-disparagement clauses into contracts to thwart bad reviews.
The new state law makes these kinds of provisions illegal, and businesses in violation of this law could face up to $10,000 in fines.
Yelp celebrated the passage of the law, calling it a victory for free speech.
California is the first state to pass legislation on the issue, but this is still a potential problem in other states.
The bill was inspired by a Utah couple whose credit score was damaged after they were fined $3,500 for unwittingly violating a retailer's "Terms of Sale" contract by posting a bad review, according to the bill's author, Assembly Speaker John Pérez.
Just last month, a New York hotel came under fire after newlyweds realized the hotel had sneaked into their contract a $500 fee for any negative reviews posted by their wedding party.
There have also been reported instances of medical and dental offices fining patients for bad reviews.