This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 112e. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
11.5 [class.union] paragraph 3 implies that anonymous unions in unnamed namespaces need not be declared static (it only places that restriction on anonymous unions "declared in a named namespace or in the global namespace").
However, 9.2.2 [dcl.stc] paragraph 1 says that "global anonymous unions... shall be declared static." This could be read as prohibiting anonymous unions in unnamed namespaces, which are the preferred alternative to the deprecated use of static.
Rationale (10/99): An anonymous union in an unnamed namespace is not "a global anonymous union," i.e., it is not a member of the global namespace.