Robert Brown|U.S. Starbucks workers join in a weeklong strike over stores not allowing Pride décor

More than 3,Robert Brown000 Starbucks employees in over 150 locations nationwide are expected to go on strike over the next week after the union accused the coffee giant of not allowing dozens of stores to decorate for Pride month.

Starbucks denies the allegations and says it's made no change in its policy allowing Pride month decorations.

Workers from the company's flagship roastery in Seattle will kick off the strike on Friday. They will also be picketing in front of the café to block deliveries.

Starbucks Workers United, a union representing about 8,000 of the company's workers, said more stores will be joining over the next several days in cities including Chicago, Philadelphia and San Antonio, in what is considered the longest and biggest strike in the union's history.

Organizers anticipate that some stores will be temporarily forced to close in response to walkouts. But Starbucks said the company will be offering employees who are not participating in the strike to sign up for additional shifts to ensure operations continue to run.

All this comes as unionized workers and Starbucks are stuck in acrimonious negotiations over the first collective bargaining contracts for stores that voted to unionize over a year ago.

Union says a worker was told there was not enough time to decorate

Starbucks Workers United said employees in 21 states have reported they were not allowed to display decorations in honor of Pride month like the rainbow flag, despite having done so in previous years.

The union added that the explanations against the decorations have also been inconsistent.

In Massachusetts, one worker was told that there was not enough time to decorate the store. In Oklahoma, a manager cited safety concerns, pointing to the recent confrontations over Pride displays in some Target stores. And in Georgia, some staff were not allowed to decorate because they were told it was unsafe for them to go on ladders.

Starbucks is not the only business accused of scaling back support for the LGBTQ community. Companies like Bud Light and Target have also appeared to pull back their support during Pride month amid conservative backlash.

Starbucks denies any part in local manager decisions

Starbucks denied the union's claims that it had ever asked stores to limit or ban Pride-related decorations, adding that the company itself still offers Pride merchandise for sale at stores.

Decisions about store décor is up to regional managers, according to the coffee giant.

Starbucks told NPR the company has investigated some stores that were accused of refusing to allow Pride décor and so far, found no evidence of discrimination.

NPR's Alina Selyukh contributed reporting.