When the taxi baron Robert Scull sold part of his art collection in a 1973 auction that helped inaugurate today’s money-soused contemporary-art market, several artists watched the proceedings from a standing-room-only section in the back. There, Robert Rauschenberg saw his 1958 painting “Thaw,” originally sold to Scull for $900, bring down the gavel at $85,000. At the end of the Sotheby Parke Bernet sale in New York, Rauschenberg shoved Scull and yelled that he didn’t work so hard “just for you to make that profit.”

The uproar that followed in part inspired the California Resale Royalties Act, requiring anyone reselling a piece of fine art who lives in the state, or who sells the art there for $1,000 or more, to pay the artist 5 percent of the resale price.

That law is now at the center of three class-action suits brought this month by artists who include Chuck Close and Laddie John Dill and the estate of the sculptor Robert Graham. They have filed suit against the auction powerhouses Sotheby’s and Christie’s and the online auction site eBay for failure to pay royalties.

“It’s a question of basic fairness,” Mr. Close said recently in an interview. When purchasers are getting extraordinary returns on their investment, he said, a royalty resale law allows the artist to share, at least in a small way, in the increase in value. (Under the California law, no payment is due if the price drops.)