Here's the low-down on a real life problem that I (or nobody else) cant seem to find a solution for. This is a very brief overview and I must necessarily withhold many of the details. The firm I am interning for this summer represents a number of labor unions. One of the unions we represent (Sheet Metal Workers) is losing work because a competing union (Carpenters) is putting the work traditionally performed by sheet metal workers into their contracts with the general contractors on jobsites. The sheet metal workers have the same work assignments in their contracts, however, the sheet metal workers have their contract with subcontractors as opposed to the carpenters union who has a direct contract with the General Contractor. The Carpenters Union is doing the same thing to other trade unions and they basically have a right to do it because the carpenters are generally the first people on a jobsite and they get the contract with the GC. If the General Contractor or subcontractor assigns any of the work to the sheet metal workers the carpenters will leave the site or impose fines on the GC.
THEORY 1: Restraint of Trade/Antitrust - Traditionally this would probably amount to restraint of trade, however, the National Labor Relations Act grants labor unions immunity from antitrust actions so long as the action takes place in the context of a collective bargaining agreement. Therefore, the Carpenter's Union are free to contract whatever the hell they want so long as it's in the context of a collective bargaining agreement.
THEORY 2: Intentional Interference with Contract - Reverts back to the problem above. The carpenters union has a right to interfere with the contract so long as their interference is based on a "good faith" belief that they have a rightful claim to the work. Since it is in the context of a collective bargaining theory they do have a rightful claim to the work.
These are the two main theories I have explored and neither would be successful. Any thoughts or ideas on other legal theories that might be successful, keeping in mind that there is probably an labor exception for theories that might normally be successful in this situation.