All Parts Part 91 Subpart H—Foreign Aircraft Operations and Operations of U.S.-Registered Civil Aircraft Outside of the United States; and Rules Governing Persons on Board Such Aircraft § 91.707
§ 91.707

Flights between Mexico or Canada and the United States

Unless otherwise authorized by ATC, no person may operate a civil aircraft between Mexico or Canada and the United States without filing an IFR or VFR flight plan, as appropriate.

Sourced from eCFR · Title 14 CFR · for educational reference only — fly the latest regs.