(Reuters) – The U.S. agency in charge of enforcing labor law on Thursday filed a complaint against electric carmaker Tesla Inc (TSLA.O), saying it found merit to workers’ complaints about unfair labor practices.

According to the National Labor Relations Board complaint, Tesla violated workers’ rights by requiring them to sign a confidentiality agreement that could bar them from talking about their working conditions and safety issues at the company’s facility in Fremont, California.

The agency also investigated charges by the workers that Tesla intimidated and harassed them and violated workers’ rights under federal labor law.

Tesla has denied the allegations.

The company must respond to the charges by Sept. 14. The NLRB has scheduled a hearing for Nov. 14 before an administrative law judge in Oakland, California.

“These allegations, which have been filed by the same contingent of union organizers who have been so outspoken with media, are entirely without merit,” Tesla said in a statement.

Complaints were filed by three employees and the United Auto Workers union, which has encouraged Tesla employees to unionize.

The workers said Tesla made them sign a document that they may face termination or criminal prosecution for speaking publicly, or to the media, about anything they observed at work or their working conditions, NLRB said.