The US Supreme Court in Washington, DC, November 6, 2013. 
The US Supreme Court in Washington, DC, November 6, 2013.  - 
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The Supreme Court hears oral arguments Wednesday in what labor experts are calling the biggest case in decades, Unite Here Local 355 v. Mulhall. At stake is a complaint filed by a Florida racetrack employee saying an agreement between the workers union and his employer violates a federal anti-bribery statute. 

Back in the day when it came to unions and employers, things were tense. Now, you could say, the two sides are more like frenemies.

"Essentially the unions are getting together with the company, and the company hands over its workers to a union in exchange for something," says Patrick Semmens, vice president of public affairs for the National Right to Work Legal Defense Foundation.

Here's how these deals work: sometimes unions promise not to picket, or they might give money to a cause the company supports. But federal labor law says employers can't give unions a "thing of value" -- that could amount to bribery.

But here's the problem, according to Harvard law professor Benjamin Sachs.

"Almost everything that unions and employers agree to, say in a collective bargaining agreement -- to raise wages or to require employees to pay dues -- could be considered a thing of value," says Sachs.

If the court rules against the union, Sachs says there's no current model for how unions will work with companies in the future.