A group of Google engineers and other workers announced Monday they have formed a union, creating a rare foothold for the labor movement in the tech industry.

About 225 employees at Google and its parent company Alphabet are the first dues-paying members of the Alphabet Workers Union. They represent a fraction of Alphabet's workforce, far short of the threshold needed to get formal recognition as a collective bargaining group in the U.S.

But the new union, which will be affiliated with the larger Communication Workers of America, says it will serve as a "structure that ensures Google workers c...