Because in America we sue over everything, a small group of Yelp users in California are suing the company, saying that they should get paid minimum wage (at least) for writing reviews for the website. Their argument begins with the premise that they are actually unpaid employees who provide value to the company without getting compensation.
See also: Is Yelp Fair to Restaurants?
The lawsuit states...
Business journal commentators have compared said [Yelp's] business practices to a 21st Century galley slave ship with pirates banging the drum to keep up the fast pace and to fill the pockets of their stockholders with treasure. . . and with "overhead that would shame an antebellum plantation." "Yelp's business model profits off the unpaid work of reviewers."
Which is probably the most dramatic way possible of describing volunteer labor, ever.
Though the lawsuit asserts that the gamification model Yelp uses to encourage reviewers to write more (things like user levels, badges, etc.), it's hard to make the leap that these incentives constitute employment. As pointed out by TechDirt, Yelpers are not hired and have no responsibilities.
Two of the four plaintiffs claim they were "fired" by Yelp since the company removed their accounts and all their reviews, but you can read the reviews from plaintiff Darren Walchesky on his Yelp profile. He's written more than 1,200 reviews.
Judge for yourself how much you think they're worth.