Newly unionized retail janitors across the Twin Cities won their first labor contract Wednesday, which will result in about 500 workers sharing an additional $4.5 million in wages over three years.

The new contract goes into effect immediately and affects the newest members of Service Employees International Union Local 26 in Minnesota, who clean Best Buy, Target, Macy’s, Cub Foods and Lunds & Byerlys stores. The janitors will receive an average 18 percent pay raise over the three years, with most seeing an immediate $1.50 per hour raise.

The janitors work for Carlson Building Maintenance in White Bear Lake, the Integrated Facility Services Group in South Carolina and Prestige Maintenance’s Major Metro subsidiary in the Twin Cities. This is the first major market in the U.S. where retail janitors are unionized.

The janitors won the right to join the SEIU over the summer after years of strikes and protests that urged several large U.S. cleaning firms and their big-box clients to improve working conditions and pay for the janitorial workers who cleaned stores each night.

The janitors had long maintained that they were subject to abuses by the cleaning firm employers. Past complaints included being forced to work seven days a week, being denied overtime pay and being ordered to change work shifts without prior notice. Several complaints landed in court and some resulted in fines issued by the Equal Employment Opportunity Commission.

In most cases, the janitorial firms denied wrongdoing, while their big-box clients such as Target urged the cleaning firms to talk to their workers and to improve relationships, work conditions and rules.

The janitors on Wednesday expressed delight in winning their first labor contract with Carlson Building Maintenance, one that will raise pay, normalize work rules and give them a voice.

Lizbet Vega Lopez, who has cleaned the Cub Foods store in Brooklyn Park for Carlson Building Maintenance for 12 years, said her pay will instantly jump from $9.50 an hour to $11.

“I am glad we stuck together and that we now have a union contract that moves us forward,” said Vega Lopez, a mother of three. “It was a big win just to get to the negotiation table with our employers, and now we have won gains that cannot be taken away.”

Union leaders praised the contract as a big win for the 500 janitors, many of whom have low incomes and are immigrants and people of color.

Maricela Flores, a contract negotiator who works for Carlson Building Maintenance at the Shakopee Target, said the contract won “big gains for our families.”

“We fought hard to get to this point, so it means so much to have won this first contract,” she said. “Especially now, it is so important to remember something we’ve said throughout our campaign: ‘When We Fight, We Win.’ ”