The U.S. Supreme Court ruling in AT&T Mobility LLC v. Concepcion may affect tens of millions of arbitration agreements in California alone, including provisions in employment agreements, consumer loan applications and cable-television contracts.

The ruling will also help companies in at least 18 states where companies now are restricted or barred from requiring consumers to accept class-action bans. "It changes the law completely" in those states, said Alan S. Kaplinsky, Chairman of Ballard Spahr's Consumer Financial Services Group.