A dispute over wages and job security for 660,000 unionized Postal Service workers was sent into binding arbitration early Wednesday after negotiators failed to meet a midnight contract deadline and called off further talks.

Union leaders accused Postal Service officials of refusing to bargain with them while Postmaster General Anthony M. Frank said the unions' demands would have "priced the Postal Service out of business."No disruption in mail service was expected because federal law prohibits postal workers from striking.

"It was a charade. We waited untold hours by the telephone for their phone calls," Vincent Sombrotto, president of the 234,000-member National Letter Carriers Union, said at a midnight news conference.

Frank, holding his own news conference minutes later, said workers' demands for a $50 billion pay increase package was an "off the wall" proposal that had derailed the collective bargaining process.

"At a time that thousands of American workers are facing layoffs or real wage and benefit reductions, the unions have insisted on unrealistic pay increases," Frank said. "Continuation of these talks at this time would not be productive."

Under federal law, a fact-finding commission will be established to review the dispute. It will report back to both sides within 45 days. If management and labor still can't reach agreement, an arbitration panel will settle the dispute.