A group representing Walmart workers laid off after the abrupt closing of five stores last week planned to seek an injunction on Monday from the National Labor Relations Board that would require the retailer to rehire all 2,200 affected workers.

Walmart said that the closings were temporary and were prompted by plumbing issues at the five stores, in California, Texas, Oklahoma and Florida. Officials at the retailer said they would do their best to rehire the workers at other stores or at the five stores once they reopened.

But a claim set to be filed on Monday by the United Food and Commercial Workers International Union with the National Labor Relations Board says that the closings were in retaliation for a history of labor activism at one of the shuttered stores, in Pico Rivera, Calif. The union is acting on behalf of Our Walmart, a group that has helped the stores’ workers air their claims, but is not a union itself.

The Pico Rivera store was the site of the first strike at a Walmart store in the United States, in 2012, organized by a workers’ group backed by the union. The strike was over pay and working conditions for the retailer’s hourly wage workers. Since then, store employees have led actions demanding changes to Walmart’s hours and pregnancy policies, access to full-time, consistent work and at least $15 an hour in pay for workers at the retailer’s 4,500 stores across the country.