Let's say you're a government contractor working on a job worth more than $25 million. Let's also say that yours is an open shop operation.

Good luck with that:

The Obama administration is set to issue a rule Tuesday that will allow federal agencies to require that contractors on large-scale public construction projects agree to union representation for workers.

The executive order, which will become effective next month, is the latest in a series of moves by the administration that are favorable to unions, whose members could play a critical role in the upcoming midterm elections as Democrats try to hang on to seats in Congress.

The rule doesn't mandate that federal agencies require contractors to bargain with unions on all jobs, but it clears the path for government agencies to make such agreements a requirement for contractors on jobs costing $25 million or more.

Labor unions applauded the new rule but builders decried it.

The order encourages the use of project labor agreements in order to promote efficiency in federal procurement.

Building trade groups said pushing contractors to agree to such agreements with unions could drive up the costs of public construction by nearly 20% and discriminate against what they said are more than the 85% of the U.S. construction workforce members who choose not to join a union.

"Anti-competitive project labor agreements are special-interest kickback schemes that end open, fair and competitive bidding on public projects," said Jim Elmer, National Chairman of the Associated Builders and Contractors and president of James W. Elmer Construction Co. in Spokane, Wash. "We will exhaust every opportunity to challenge this policy, which is effectively a federal government endorsement of union set-asides."