I don't know what you mean by "obligation," but I assure you employers have a legal duty to negotiate in good faith with their employees' representative. See 29 U.S. Code § 158 (a)(5) - It shall be an unfair labor practice for an employer...to refuse to bargain collectively with the representatives of his employees, subject to the provisions of section 159(a) of this title.
> employers have a legal duty to negotiate in good faith with their employees' representative
Sure thing. But that typically takes place in scheduled sessions. Casting Starbucks as refusing to engage when they’re adding it to the next meeting’s agenda is what I’m pushing back against.
