British regulators blocked Microsoft's purchase, thwarting the biggest tech deal in history over worries that it would stifle competition in the fast-growing cloud gaming market.

The Federal Trade Commission said Microsoft's planned takeover of the video game company could suppress competitors to Microsoft's Xbox game consoles and its growing games subscription business.

Activision Blizzard is behind huge games such as Call of Duty, World of Warcraft, and Candy Crush. But the company has faced reports of a workplace culture rife with sexual harassment.

Union supporters say the companywide email to employees of the video game giant is an effort to intimidate workers into dropping the union push amid a sexual harassment and equal pay controversy.

The game giant behind Call of Duty and World of Warcraft settled with the U.S. Equal Employment Opportunity Commission after the agency filed a civil rights lawsuit over the company's culture.