I hesitate to disagree with G but this is in CS-23 amendment 3:
CS 23.1527 Maximum operating altitude
(a) The maximum altitude up to which operation is allowed, as limited by flight, structural, powerplant, functional, or equipment characteristics, must be established.
(b) A maximum operating altitude limitation of not more than 7620 m (25 000 ft) must be established for pressurised aeroplanes, unless compliance with CS 23.775 (e) is shown.