Microsoft's surprise $68 billion deal to buy Activision Blizzard is adding a fresh twist to the heated debate over which tech companies have monopolies that need to be reined in.

The big picture: The deal could force a question the company has happily ducked for a decade: whether its size and power make it just as deserving of regulatory scrutiny as its Big Tech rivals.

Why it matters: Regulators have finite resources and will have to prioritize which companies and deals they want to contest.

Flashback: Microsoft, of course, spent years fighting a Justice Department antitrust suit two decades ago — but in the most recent wave, regulators have largely focused on Apple, Google, Amazon and Facebook.

Between the lines: Microsoft will argue that, in the mobile age, Apple and Google hold a dominant market position with their tight control over mobile app stores.

• For game developers and others, though, Microsoft may well look like the firm whose grip over some parts of the consolidating gaming world is too tight.

The key question is how the regulators at the Federal Trade Commission and other agencies, who will ultimately decide whether the deal can go forward, choose to define the markets it affects.

Of note: On Tuesday the Justice Department and Federal Trade Commission announced the start of a process that will ultimately result in rewritten merger guidelines, which could translate as more hurdles for large deals.

• The agencies are seeking public comment on modernizing enforcement of antitrust laws around mergers, with a focus on whether previous guidelines leave out certain aspects of competition.
• One focus of the agencies' questions: whether guidelines should be different for digital markets.
• Neither agency is commenting specifically on the Microsoft-Activision deal.

Be smart: A good antitrust case, or a decision to block a deal, isn't determined by people's feelings or a company's size. It's about whether a company has, or with acquisitions could gain, undue control over a relevant market.

• "It's important to remember that a large dollar value doesn’t always mean competitive concerns, just as a small deal can raise antitrust problems," says Daniel Francis, the former deputy director of the FTC Bureau of Competition.
• "The agencies will look closely at whether the Microsoft-Activision deal threatens to create market power or eliminate competitive pressure in any market," Francis told Axios.

Microsoft is counting on the fact that even with the deal, it will have less than 15% of video game industry revenue, trailing both Tencent and Sony. But regulators may choose not to look at the broad "gaming" market as a whole, and instead distinguish between mobile, console, PC and cloud gaming.

• The Microsoft deal will certainly strengthen Microsoft's position in console gaming. But Microsoft trails Sony and Nintendo there, and mobile is growing faster, potentially overshadowing concerns over console strength.

Between the lines: Microsoft hasn't entirely escaped the latest tech antitrust surge, with some critics raising concerns about its move to integrate Teams into Office and Windows.

• "It is not yet clear whether regulators will seek to restrict Microsoft’s activity in the same way they are seeking to restrict the activity of other Big Tech firms," New Street Research said in a note Tuesday. "This acquisition will shed light on that issue."

What they're saying: Rep. Ken Buck (R-Colo.), whose office has been pushing tighter regulation of other Big Tech companies, says conversations with Microsoft were "encouraging," while noting the deal still faces agency review.

• "They've suggested that they're going to emphasize access to titles and competition in the marketplace as well as the individual gaming experience," Buck said in a statement.

Public Citizen is calling for regulators to quash the deal.

• "Microsoft, one of the biggest of the Big Tech companies, is shamelessly gobbling up a competitor to try to strengthen its market position," said Alex Harman, the group's competition policy advocate. "If Microsoft wants to bet on the 'metaverse,' it should invest in new technology, not swallow up a competitor."