Congress passed a law making ALL days of September regular holidays. Constitutional?


No, it is unconstitutional.

No person shall be deprived of property without due process of law. Due process has two aspects: substantive and procedural. As required by substantive due process, the law must not be unreasonable or unduly oppressive.

The right of employers to reasonable return on investment is a property right protected by the due process clause.
In this case, the making of all 30 days of September as regular holidays has an effect of compelling employers to pay their employees twice their salary as a consequence of the holiday pay law. LAW 123 appears to have been passed for an unreasonable purpose and, as a result thereof, capital's property rights are unduly oppressed.