A man dressed up as Ronald McDonald takes part in a protest outside a McDonald’s restaurant in Manhattan in March to demand higher wages for fast- food workers. (Reuters/Carlo Allegri)

Over the last few years of the union-backed drive for higher wages at fast-food restaurants, many commentators have noted the protests‘ impact on public perception: The idea of paying $15 an hour no longer seems quite so outlandish as it used to.

But it became apparent Friday that the campaign had been working toward a subtler victory — and one that’s potentially far more important.

Behind the battle in the streets is a battle in the courts. Every time workers see their hours cut or are fired for showing up at a protest, the various committees affiliated with the “fight for $15″ file charges with the National Labor Relations Board. There were so many filed against McDonald’s in particular, and they were so similar in nature, that the NLRB decided to consolidate 78 of them into 13 complaints that treat the company as a “joint employer” with its franchisees.

Why is that so crucial? As we’ve explained before, being a joint employer would make McDonald’s liable for the labor violations of the “small businesses” that operate under its brand. And you wouldn’t think it would be such a huge lift for McDonald’s to ask its franchisees to obey the law.

But here’s the problem for the golden arches: If the company is now also an employer of all those fry cooks and cashiers, it would become much easier for employees to organize a union, since the bargaining unit could potentially include all McDonald’s employees, not just those of each individual franchise. And that’s what the company will go to extreme lengths to avoid. (Another McDonald’s-related case scheduled to be decided any day now, this one involving subcontractors, could have a similar and even more far-reaching effect.)

The reason the NLRB’s general counsel thinks that McDonald’s is a joint employer with its franchisees ultimately comes down to the fact that, through the terms of its contract, the company substantively controls the experience of being a worker in one of its restaurants. But in a fact sheet accompanying the announcement, general counsel Richard F. Griffin Jr. also identified another reason why he thinks McDonald’s is acting like an employer: “This finding is further supported by McDonald’s, USA, LLC’s nationwide response to franchise employee activities while participating in fast food worker protests to improve their wages and working conditions.”

In other words, according to the NLRB, the fact that McDonald’s franchisees displayed a pattern of retaliation against protesting workers — allegedly by placing them under surveillance, cutting their hours, etc. — indicates that the company itself was coordinating the response. The general counsel didn’t lay out evidence that would back that up. But he could be holding such evidence for trials, which will begin in March.

Now, it could be a very long time before the plaintiffs in the case see any resolution. On a call after the complaint was issued, the International Franchise Association — which has been fighting the joint employer idea fiercely ever since the general counsel made his philosophy clear in July — declared that the struggle was just beginning.

“From IFA’s perspective, nothing is off the table,” said Robert Cresanti, the association’s executive vice president. McDonald’s itself also said it would “contest the joint employer allegation as well as the unfair labor practice charges in the proper forums.”

Theoretically, that could go all the way up to the Supreme Court. The NLRB can’t order monetary damages — all it can do is make employers give fired workers their jobs back, along with lost wages, if the worker is still around to take the job. But over the long run, the potential for employees to organize means the wages of future McDonald’s workers could rise quite a bit.