Synonyms for With reference to:

adj.

concerning (adjective)
regarding.
regarding (adjective)
in relation to.

n.

with reference to (noun)
concerning, in regard to, in relation to, regarding, vis-a-vis, with respect to, related, as to, with regard to, related to.

prep.

apropos (preposition)
as to, with respect to, concerning, regarding.
concerning (preposition)
in regard to, with regard to.

Other synonyms:

concerning
concerning.
regarding
regarding.