The Boeing Co. violated the National Labor Relations Act in April when a human resources manager at its North Charleston complex told a mechanic there not to talk about unionizing during working time, an administrative law judge has found.

Boeing Co. cannot prohibit employees from discussing the union while allowing discussion of nonwork-related matters during working time, explained Judge William Nelson Cates.

Cates, who conducted a trial in the case last month, ordered Boeing to stop that prohibition and required the airframer to post a notice at the facility that notifies employees of their right to organize.

A spokeswoman for the Boeing Co. said the company is “disappointed” with the decision and disputed the findings.

“Boeing does not — and has not — told any employee that he or she can’t talk about the union (or any other subject) during work time, as long as the discussions don’t impact production,” Candy Eslinger, the spokeswoman, wrote in an emailed statement.

“To the contrary, we encourage our South Carolina teammates to carefully consider the impact that a union would have on their relationship with management, and talking about the IAM’s attempt to organize Charleston is an important aspect of their decision-making.”

Representatives of the International Association of Machinists and Aerospace Workers brought the unfair labor practice charge on behalf of the mechanic this spring and, did not respond to messages Saturday.

According to the allegations in the case, Ronald Bourrillion, a pro-union construction mechanic in the mid-body factory, was chastised for promoting the union during working hours.

Bourrillion said he only talked about the union during break time.

The National Labor Relations Board had accepted the charge in April, issued a complaint in late June and argued the case on behalf of the union and Bourillion last month.

The decision comes amid an intensifying International Association of Machinists organizing drive at Boeing South Carolina.

The local International Association of Machinists representative said this month that “greater than 50” Boeing workers had signed up and that an NLRB election could happen within a year.