When Los Angeles City Council members voted two years ago to give hotel workers a raise, Bill Martinez was the type of worker they said they wanted to help. Martinez, a 53-year-old bellhop, has hauled tourists’ luggage across the flagstone plaza of the Sheraton Universal in Studio City for two decades. He said he was excited after the council’s vote to raise the minimum hourly wage at large hotels to $15.37, which he expected to boost his paycheck by 71%.

He soon found out he wouldn’t be getting a raise after all. Under an obscure provision of the city’s wage hike, unionized hotels were granted an exemption allowing them to pay their employees less. The result is that Martinez, who pays $56.50 every month for membership in the hotel workers union Unite Here, now makes less than those doing the same job in non-union workplaces. “That’s what really makes me mad,” Martinez said. “I just wanted to be treated equal. Don’t exempt us, because we’re the ones paying union dues.”

Few progressive causes have enjoyed as much recent success as the campaign to raise pay for the working poor. Most large cities in California have raised their minimum wage over the last several years, culminating in Gov. Jerry Brown’s signing the nation’s first statewide $15 minimum wage last week. On the same day, New York enacted a less-comprehensive wage increase that activists also greeted as a victory.

Less celebrated, and often unnoticed, has been a series of loopholes that cut union workers out of the very pay increases their leaders have championed. Such clauses have emerged as one of the labor movement’s most divisive issues, clouding an otherwise triumphant political moment for the unions that have backed new wage mandates.

Counterintuitive at first glance — organized labor’s historic goal has been to obtain more for workers, not less — union exemptions are absent from state and federal pay standards. Yet they have been written into the fine print of wage ordinances in a dozen California cities at labor leaders’ urging. San Francisco, San Jose, Oakland and Santa Monica have all adopted union waivers in their most recent minimum wage laws. L.A. city officials are expected to indicate whether they will include such an exemption in their own $15 minimum wage at a hearing next week.

Critics see such provisions as a cynical collusion between politicians and big-city labor interests. By making unions the “low-cost option” for businesses seeking to avoid paying better wages, they assert, the exemptions are designed to drive up union membership — and revenue from dues — at the expense of workers.

The disparities bred by union minimum wage waivers are stark. At the Sheraton Universal Hotel, a longtime union property, bellhops, waiters and banquet servers make California’s current minimum wage: $10 an hour. Those doing the same jobs at a non-union Hilton less than 500 feet away make at least $15.37 under the city’s hotel wage law. Neither amount includes tips.