14 CFR § 103.17
Operations in certain airspace
July 13, 2020
No person may operate an ultralight vehicle within Class A, Class B, Class C, or Class D airspace or within the lateral boundaries of the surface area of Class E airspace designated for an airport unless that person has prior authorization from the ATC facility having jurisdiction over that airspace.
[Amdt. 103-17, 56 FR 65662, Dec. 17, 1991]