SoftBank Group Corp. Chairman Masayoshi Son has battled for years to merge T-Mobile U.S. Inc. with his Sprint Corp. Now that he finally has a deal, he risks having his hands tied by a secretive U.S. government panel.

The merger between T-Mobile and Sprint would join the third- and fourth-largest U.S. wireless providers. The new company would be majority owned by foreign investors — one German and one Japanese — triggering a review by the Committee on Foreign Investment in the U.S. for any possible threats to national security.

That creates an added — if familiar — hurdle for SoftBank beyond scrutiny by U.S. regulators on antitrust and public interest grounds. If the security panel has concerns, it could impose conditions on the $26.5 billion deal, including limits on supply chains, governance and information sharing, as well as requiring tighter cybersecurity defenses, according to lawyers who work on security reviews of deals.