Starbucks Corp. filed two complaints with the U.S. National Labor Relations Board alleging unfair practices by labor organizers toward workers and what it calls “an increase in nefarious behavior.”

The coffee chain says individuals associated with Workers United, which is leading unionization efforts, limited access to stores in Arizona and Colorado and threatened workers for not supporting the labor drive. They also yelled profanities, surrounded stores and pounded on windows, according to the complaints and a letter from Rossann Williams, the company’s North American president.

These incidents “we believe have crossed the line and we have filed an unfair labor practice charge with the NLRB,” Starbucks said in an email.

Starbucks appears to be taking a more aggressive approach to the broadening unionization effort across the U.S. after founder Howard Schultz’s return as interim chief executive officer. The union has also filed dozens of NLRB complaints against the company alleging illegal behavior, which Starbucks has denied.

Some of the union’s accusations have advanced, and labor board prosecutors plan to formally accuse Starbucks of illegally firing a group of activists who’ve been trying to unionize their store in Memphis, Tennessee, unless the company first settles the case.

Starbucks said the employees were punished because they let off-duty staff and non-employees, including reporters, into their store when it was closed, and violated numerous safety rules — not because they were labor activists.

In an email, Workers United said the charges are “a continuation of Starbucks’ war against its own partners” and a sign of “desperation” as the company “loses this war in battle after battle.”

Workers United is an affiliate of the Service Employees International Union.