With thousands of workers, and estimated sales in the hundreds of millions, California’s medical marijuana industry has never been bigger. Now, with a ballot measure to legalize recreational pot use for adults gaining in the polls, some of the state’s most powerful labor unions are “growing” their membership.. by going to pot. At Oakland’s Patient ID Center and head shop, manager Chad Gilmore says the staff is grateful to have organized labor on their side. “Unionizing is giving us representation,” he says, “and representation is what employees in the standard industry needed these days.”

Just like employees in other service industries, Gilmore says he and his 13 co-workers want to be able to negotiate collective bargaining agreements, get pensions, vacation time, and health benefits. He adds, the staff welcomes the legitimacy that union representation brings to an industry that isn’t always seen in a favorable, or legal, light. They can’t count on getting workplace protections or benefits under federal workplace laws.

While 175 workers have joined the local United Food & Commercial Workers Union, about 40 clippers, trimmers, and cloners for Oakland-based Marjyn Investments LLC have teamed up with the Teamsters Local 70. It’s the country’s first group of unionized marijuana growers, and “a win-win for everyone,” says the company’s attorney, Clinton Killian. “The workers get the benefits, and we get a very stable workforce.” Among other things, the worker’s current wages of $18.00 per hour will increase to $25.75 an hour by 2012.

The trend has critics shaking their heads.

Anti-pot crusaders say these labor groups are misguided, and doing their newest members a disservice by encouraging them to do work that’s considered a federal crime. “I think to help your workers do something that’s criminal to begin with is wrong, and their workers need to find a way to make a living without doing something completely illegal,” says Roger Morgan, executive director of the Coalition for a Drug Free California. He says instead of getting benefits, “California’s pot workers should be sanctioned.”

But experts say it’s easy to understand why unions are taking more than a budding interest. “It’s not a surprise to me that the United Food & Commercial Workers and the Teamsters would say, here’s an area where there’s potentially going to be job growth, an area where workers want representation, it’s a logical place to go,” says Ken Jacobs, chair of the Center for Labor Research and Education at UC Berkeley.

If voters legalize marijuana next month, labor experts predict even more unions will get involved– not just as negotiators for employees, but allies for the marijuana growers, as the industry fights the legal challenges certain to come from the federal government.