The National Labor Relations Board on Monday shortened the time frame for union representation elections, putting into effect a rule that businesses have vigorously opposed.

The so-called "ambush" shrinks the time between a petition for a union election and the voting itself from what Associated Builders and Contractors says is the current average of 40 days to a period of 17 to 20 days.

"The shortened time period for union elections will place a premium on rapid response by employers to union organizing activity," ABC warned its members. The rule immediately affects only companies that are in the process of having a representation election.

ABC leads the Coalition for a Democratic Workplace, which has sued to stop the rule.

Monday, NLRB Chairman Mark Gaston said, "The modest and sensible changes taking effect today will provide efficiency and savings to all parties involved in the election process."