Workers at two U.S. companies have filed cases with the National Labor Relations Board challenging changes to their working conditions spurred by the Covid-19 pandemic.

A tea shop in Colorado, Ku Cha House of Tea, is facing an “unfair labor practice” charge, filed Thursday, after it replaced six employees, allegedly because they organized to negotiate safety precautions related to the coronavirus, according to the charge. Valerie Collins, an attorney with Towards Justice who’s involved in the case, provided a copy of the charge to Bloomberg Law. The company said it had to let the workers go because they refused to return to work and it needed to open for business.