Thousands of Amazon workers have ended their days-long strike against the company, according to the Teamsters union. But tensions persist, with the union saying its efforts aren’t over.

The International Brotherhood of Teamsters announced their support of an Amazon worker strike that started Thursday after the company didn’t meet the union’s deadline for bargaining negotiations with protesters.

With Christmas two days away, workers at four Amazon warehouses in Southern California are on strike Monday on claims the corporate giant refuses to recognize their union and negotiate fair contracts.