FORTRAN does not allow implicit aliasing between distinct function/procedure arguments, which helps optimization.

It allows explicit aliasing using the EQUIVALENCE statement, which declares that 2 variables of arbitrary types and names are allocated at the same memory address.

The C language has taken the keyword "union" from the language ALGOL 68, but instead of implementing true unions like in the original language (i.e. with tags handled by the compiler and with type safety) it has implemented a version of the FORTRAN EQUIVALENCE, which however is also weaker and less convenient than the FORTRAN declaration (unlike C's union, FORTRAN's EQUIVALENCE also worked for aliasing parts of bigger data structures, e.g. sub-arrays).

Fortran doesn't disallow aliasing per se of dummy arguments to functions or subroutines, but we do restrict what can be done with aliases in many cases. The details matter.