LOS ANGELES (Reuters) - The Screen Actors Guild said on Sunday its board had voted to have a federal mediator brought into labor contract negotiations with Hollywood studios.

The guild also said it would ask its 120,000 members to authorize a strike if the arbitration process fails. A strike authorization would require 75 percent approval of members who vote.

Talks with Hollywood studios broke off on June 30 when the Alliance of Motion Picture and Television Producers presented the actors union with a "final" offer, hours before the old contract lapsed.

"No matter what SAG does - whether it be authorizing a strike or following a different approach - it will not change the harsh reality that currently confronts our industry," the studio group said in a statement.

At issue is a new contract covering union performers in prime-time TV and movies. The two sides are at odds over how actors should be paid for content delivered over the Internet and whether all made-for-online productions should be subject to the union's contract.

The studio offer essentially mirrors terms approved by several other Hollywood unions, including the settlement that ended a 14-week stroke by Hollywood screenwriters in February.

Union leaders have pressed to reopen negotiations, but the studios have refused.

"We hope mediation will help move this process forward," Screen Actors Guild's national president, Alan Rosenberg, said in a statement.

The studio alliance repeated on Sunday "there is simply no justification for SAG to expect a deal that is in excess of what the other Guilds negotiated in better economic times."

The union also said four new members have been added to its national negotiating committee -- two from the Hollywood division, one from the New York division and one from the regional branch division.

The last time SAG staged a strike over its main film and TV contract was in 1980, a walkout that lasted three months.