Lina Khan, the seat of the Federal Trade Commission, has pledged to usher successful a caller epoch of trustbusting of America’s firm giants, precocious saying the bureau plans to “enforce the antitrust laws to guarantee maximal efficacy.”

Now Ms. Khan has staked that ambitious agenda connected a lawsuit that whitethorn beryllium highly challenging for the bureau to win.

The F.T.C. connected Thursday sued to artifact Microsoft’s $69 cardinal acquisition of the video crippled steadfast Activision, the biggest user tech woody successful 2 decades. The enactment punctuated Ms. Khan’s statements astir reining successful firm power and was the boldest of a caller drawstring of lawsuits from the bureau to forestall other, smaller deals successful the sanction of competition.

But Ms. Khan and the F.T.C. look hurdles successful trying to halt the Microsoft-Activision deal, experts said. That’s due to the fact that courts person been skeptical of challenges to alleged vertical mergers, wherever the 2 businesses don’t vie directly. In this case, Microsoft is champion known successful gaming arsenic the shaper of the Xbox console, portion Activision is simply a large steadfast of blockbuster titles specified arsenic Call of Duty.

In addition, Microsoft has made a fig of concessions to trim regulatory concerns astir buying Activision — specified arsenic pledging that Call of Duty would beryllium disposable connected Sony’s PlayStation and Nintendo’s platforms, and not conscionable connected Xbox — which immoderate judges whitethorn find persuasive.

“It’s undeniably a challenging suit for the commission, due to the fact that vertical challenges mostly person an uphill battle,” said Bill Baer, who led the Justice Department’s antitrust part during the Obama medication and has represented Sony successful backstage practice.

The lawsuit is shaping up arsenic a trial of Ms. Khan’s content that the F.T.C. indispensable go much assertive to cheque the powerfulness of firm giants successful the modern economy, including the biggest tech companies. Appointed to pb the bureau by President Biden, she has signaled she wants to instrumentality much lawsuits to tribunal — alternatively of settling with companies — to push the boundaries of antitrust law and instrumentality to the benignant of trustbusting not seen since the past century.

Since Ms. Khan took implicit the F.T.C. successful June past year, the bureau has employed caller oregon little-used arguments to situation deals. It sued to artifact the merger betwixt the spot makers Nvidia and Arm, different woody successful which the companies were not nonstop competitors. In July, the bureau sued to halt Meta, Facebook’s genitor company, from buying the virtual world start-up Within, successful a lawsuit that hinges connected an uncommon statement that the woody would harm contention successful a marketplace that hasn’t developed yet.

Microsoft has vowed to combat the F.T.C.’s suit against the Activision purchase. On Thursday, Brad Smith, Microsoft’s president, said the institution had “complete assurance successful our lawsuit and invited the accidental to contiguous it successful court.” On Friday, Microsoft pointed to erstwhile statements that it believes the woody would grow contention and make much opportunities for gamers and crippled developers.

An F.T.C. spokesperson declined to remark connected the case.

Regulators person traditionally focused connected challenging mergers that harvester 2 nonstop competitors. When they person brought lawsuits against vertical mergers, their grounds has been mixed.

The biggest and astir bruising caller conflict implicit a vertical merger was successful 2017, erstwhile the Department of Justice tried to artifact AT&T’s $85.4 cardinal acquisition of Time Warner. A national justice yet allowed the woody to spell forward, saying helium was unconvinced the operation would harm contention successful telecommunications and media.

This year, a justice ruled against the F.T.C.’s effort to stop a gene-sequencing company from buying the shaper of a crab humor test, saying the grounds hadn’t proved that the gene-sequencing institution would person an inducement aft the acquisition to harm competitors of the blood-testing product.

But Ms. Khan, on with her counterpart astatine the Justice Department, has spearheaded an effort to rewrite the guidelines for assessing specified deals.

The F.T.C. has chiefly based its lawsuit against Microsoft’s Activision woody connected the thought that the Xbox and PlayStation consoles vie successful a league of their own, and not against different video gaming devices similar the Nintendo Switch. Barry Nigro, who worked successful the Justice Department’s antitrust part during the Obama administration, said the courts would heavy see whether that explanation was close successful deciding the case.

In its complaint, the F.T.C. argued that the games that Activision made were “extremely important” for the occurrence of video crippled consoles, truthful Microsoft would person the quality and inducement to usage its power of those titles to support them from competitors oregon degrade their quality.

Microsoft has repeatedly said it would not marque consciousness to instrumentality Call of Duty disconnected PlayStation, wherever astir gamers play the game. This week, Microsoft signed a 10-year statement to bring the crippled to Nintendo’s Switch, and has said it offered Sony a akin arrangement.

But the F.T.C. dismissed Microsoft’s promises. It pointed to a $7.5 cardinal deal that Microsoft closed past twelvemonth to bargain ZeniMax, the genitor institution of 8 crippled studios that marque deed franchises similar The Elder Scrolls, Doom and Fallout.

The bureau wrote successful its ailment that Microsoft had “assured” regulators successful Europe who were reviewing the ZeniMax woody that it would not person an inducement to withhold ZeniMax titles from rival consoles. But Microsoft aboriginal announced that large caller games from ZeniMax’s studios would beryllium released lone connected its Xbox and Windows computers.

That should “cast much suspicion” connected Microsoft’s statements astir keeping Call of Duty disposable connected PlayStation, the bureau said successful its lawsuit.

Microsoft has said those caller ZeniMax games cannot beryllium compared to an existing franchise similar Call of Duty. It has indicated that the F.T.C. is misrepresenting what happened due to the fact that the institution made nary commitments to the European Commission, pointing to European filings successful which it said it would determine however to merchandise games connected a “case-by-case basis.”

In meetings with the bureau and commissioners connected Wednesday, Microsoft offered to marque enforceable, bound commitments to support Call of Duty connected PlayStation, a idiosyncratic with nonstop cognition of the conversations said. But the commissioners did not look funny successful accepting a settlement, the idiosyncratic said.

The F.T.C. declined to remark connected conversations it had with Microsoft earlier the lawsuit.

Those types of agreements person fallen retired of favour with regulators similar Ms. Khan. She has said promises that companies marque to regulators are seldom enforced and don’t code halfway problems of companies getting bigger and exerting their powerfulness to harm competition.

Judges successful immoderate caller antitrust cases person cited colony offers arsenic a crushed to let mergers to proceed implicit regulators’ objections. “Courts person been amazingly solicitous astir the benignant of things that Microsoft has offered here,” said Daniel Francis, an adjunct prof of instrumentality astatine New York University and a erstwhile F.T.C. official.

The F.T.C. ailment said the archetypal proceeding successful the lawsuit would beryllium successful August.

Kellen Browning contributed reporting.