Obama called for "a swift and smooth resolution" of the dispute. More than 400 workers went on strike at midnight.
Workers will have to return to the job when the board is established at 12:01 a.m. Sunday. Obama's order doesn't force the two sides to resume direct talks with each other. But they must participate with the board's process, which typically involves written submissions and hearings.
After 30 days, the board must recommend to Obama how the dispute should be resolved.
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