osporavati

1. to dispute; to contest; to deny
   Opozicija osporava rezultate izbora. — The opposition is disputing the election results.
   Niko ne osporava da je on talentovan. — Nobody denies that he is talented.
2. (sth to sb) to deny someone the right to something
   Ne osporavam ti pravo na tvoje mišljenje. — I don't deny you the right to your opinion.

The perfective is osporiti.