SARAJEVO, Bosnia-Herzegovina — Defying the country’s constitutional court, Bosnian Serbs said Monday they will hold a referendum on a disputed national holiday in their autonomous region.

The Sept. 25 referendum will ask residents of Bosnia’s Republika Srpska region whether they agree the ‘statehood’ day of the Serb mini-state should remain Jan. 9. The Court ruled the date discriminates against Muslim Bosniaks and Catholic Croats since it falls on a Serb Orthodox Christian holiday.

Bosnian Serbs declared in 1992 the creation of their own state within Bosnia on Jan. 9, which is the traditional Serb Patron Saint’s Day. During the war that followed, they expelled non-Serbs from the territory they controlled with the aim of making it part of neighboring Serbia. Although Republika Srpska ended up not independent but an autonomous region of Bosnia, they still celebrate Jan. 9 as a national holiday. For non-Serbs living there the date is a symbol of their expulsion and a sign that Republika Srpska is still a place meant just for Serbs.

The court banned the referendum on Saturday but Bosnian Serb prime minister Zeljka Cvijanovic said Monday it will be conducted anyway. Bosniaks fear the disputed referendum is a test for a more serious one in 2018 — on Republika Srpska’s independence from Bosnia.

Western officials have urged Republika Srpska to cancel the vote as it challenges the rule of law and Bosnia’s peace agreement. The U.S. embassy in Sarajevo threatened “consequences” without specifying what those would be. An international body overseeing the implementation of Bosnia’s peace accords, the Peace Implementation Council, stated earlier no part of Bosnia has the right to secede. The Russian representative withdrew support for the statement, siding with the Serbs.

Russian support for the referendum was reaffirmed Monday by the Russian ambassador to Bosnia during a meeting with Bosnian Serb leader Milorad Dodik, according to a statement from Dodik’s office. The two discussed Dodik’s meeting with Russian President Vladimir Putin in Moscow on Thursday.

Conducting the referendum would now be a criminal act against the constitution but Cvijanovic said Monday the entire Bosnian Serb parliament backed the decision, expressing doubt anyone would arrest the entire parliament, all the ministers of the Bosnian Serb government and every voter.