It's not legal in the U.S., where union organizing is protected under law. The beginning of the article says:

"Google unlawfully fired employees for attempting to organise a union, a US federal agency has said.

A complaint filed by the US National Labor Relations Board (NLRB) alleged that Google unlawfully monitored and questioned its employees about their union activity."

Illegal but also very possibly without consequence. The NLRB has no independent enforcement power, sadly: https://www.nlrb.gov/about-nlrb/what-we-do