(Reuters) - Alphabet's Google is facing a second complaint from a U.S. labor board claiming that it is the employer of contract workers and must bargain with their union, the agency said on Monday.

The complaint issued by the National Labor Relations Board last week claims that Google is a "joint employer" of about 50 San Francisco-based content creation workers employed by IT firm Accenture Flex who voted to join the Alphabet Workers Union in 2023, according to board spokeswoman Kayla Blado.

Blado said the board is separately investigating an October complaint by the union that Google and Accenture Flex made changes to working conditions without bargaining first.

A finding that Google is the joint employer of workers provided by Accenture Flex would force the company to the bargaining table and make it liable for any violations of federal labor law.

The labor board in January 2024 ruled in a separate case that Google was required to bargain with a group of workers at YouTube Music, which it owns, who were employed by a different staffing firm. A U.S. appeals court will hear Google's appeal of that decision later this month.

The tech giant has said it does not exert enough control over contract workers to be considered their joint employer. The company last year eliminated a $15-an-hour minimum wage for contractors and made other changes designed to avoid having to bargain with unions.

The new complaint will be heard by an administrative judge whose decision can be reviewed by the five-member board.

Google and the Alphabet Workers Union, an affiliate of the Communication Workers of America union, did not immediately respond to a request for comment.

Google has faced an uptick in labor organizing in the United States and abroad in recent years, including a series of worker protests over the company's business and employment policies.

The standard for determining when businesses are joint employers of contract and franchise workers has been in flux since the Obama administration.

A 2024 NLRB rule that made it easier to hold companies liable as joint employers was struck down in court, and appointees of Republican President-elect Donald Trump are expected to replace it with a more business-friendly standard.