anti-republican
adjective
an·ti-re·pub·li·can 
ˌan-tē-ri-ˈpə-bli-kən,
ˌan-tī- : opposing or hostile toward republicanism or republican forms of government
The obvious connexion between Germany's secret rearmament in 1923 and the growth of anti-republican forces is also documented … 
The Times Literary Supplement (London)
The Times Literary Supplement (London)
Word History
First Known Use
1716, in the meaning defined above