Mr. Trump's recent executive order targeting transgender people contains the following clause:
(d) The Secretaries of State and Homeland Security, and the Director of the Office of Personnel Management, shall implement changes to require that government-issued identification documents, including passports, visas, and Global Entry cards, accurately reflect the holder’s sex, as defined under section 2 of this order; and the Director of the Office of Personnel Management shall ensure that applicable personnel records accurately report Federal employees’ sex, as defined by section 2 of this order.
This has reportedly already begun to be implemented within the State Department, with Rubio directing employees to "suspend" all passport applications seeking a change of gender marker, and to cease issuance of passports with an X gender marker.
I recall that Zzyym v. Blinken was the origin of the X gender marker on passports, based on the Administrative Procedure Act and an equal protection claim. Naively, it would seem this order would be subject to the same scrutiny, but I haven't seen any discussion of this. Is there something I'm missing, or should we expect this order to be challenged under similar grounds?