Two security officers who work on the Amazon campus in Seattle say their hours were cut after they marched to the company's headquarters on May Day.
The Service Employees International Union filed a complaint Wednesday to the National Labor Relations Board on behalf of Abdinasir Elmi and Betiel Desta.
Elmi and Desta are employed by Security Industry Specialists, a California-based company that contracts with Amazon.
"This problem has been going on for a long, long time. This is not the first time," Elmi said.
The struggle between SEIU and SIS goes back to 2012 when Amazon switched to SIS from a different contractor.
SEIU has been trying to organize the security officers since then. Wednesday's complaint is one of several that have been filed since.
SEIU and some of the officers say that SIS has been too aggressive in opposing the union. The company has also been criticized for not accommodating its Muslim workers who allege that they have not been given time and space to pray.
"There's a lot of people who work for SIS and there's a lot of people going through all these things that we're talking about," Betiel said. "We're basically just asking for basic rights."
SIS President and Chief Financial Officer Tom Seltz said there are more than 1,000 SIS employees in the greater Seattle area.
Seltz denied the retaliation charges in an email. He also said that prayer spaces for Muslim security officers has been made available.
"I can say that we have never retaliated against employees for participating in a demonstration, attempting to form a union, etc.," Seltz wrote.