Bosnian Serbs have reacted furiously to a ban on genocide denial imposed by the international official overseeing Bosnia's 1995 peace deal.
UN-appointed High Representative Valentin Inzko said the ban was needed to stop glorification of war criminals.
"I had to do something - I followed my conscience. If you're in a country where war criminals are glorified, this cannot be a good future," he said.
Bosnian Serb politicians are boycotting Bosnia's multi-ethnic national bodies.
Last month the genocide conviction of Bosnian Serb wartime commander Ratko Mladic was confirmed in The Hague, yet some ethnic-Serb leaders were still acclaiming him as a hero. So Mr Inzko, an Austrian diplomat, said he had to act.
Milorad Dodik, the Bosnian Serb member of the country's joint presidency, says he will not accept the amendments to the criminal code.
He has launched a petition claiming that the Srebrenica massacre was not an act of genocide - yet such denials may now be punished with a maximum prison sentence of five years.
Mr Dodik may now stir up feelings of victimisation in the Serb territory, Republika Srpska.
But Valentin Inzko, just days away from leaving office, is unfazed.
"These reactions were expected," he told the BBC. "Maybe there will be more graffiti for a short period. But maybe soon there will be less, or it will stop. The posters of Ratko Mladic put up in Srebrenica this week have already disappeared."
Under the peace settlement, the High Representative has powers to dismiss politicians, push through laws and veto others.