Lawmakers in Bosnia's autonomous Serb region of Republika Srpska have voted to hold a referendum on the authority of the national court over its people.
Regional President Milorad Dodik had proposed the referendum, arguing that the court is biased against Serbs.
Bosnia-Herzegovina was divided into two entities after the 1992-1995 war: the Serb-run Republika Srpska and the Bosniak-Croat Federation.
Critics fear the referendum will undermine Bosnia's tenuous stability.
Of Republika Srpska's 83 MPs, 45 voted in favour of the referendum while 31 abstained and the rest did not take part.
Mr Dodik said the vote was "about whether we are going to go the way of preserving the constitution and defending our international right, or the way of degrading Republika Srpska."
In his speech to the regional parliament, he complained that the country's prosecutors had been more lenient towards "the few Bosniaks" charged with war crimes compared with Serbs.
But the move was criticised by the High Representative for Bosnia-Herzegovina, Valentin Inzko, who is responsible for ensuring the Dayton peace accord, which ended the war, is adhered too.
Mr Inzko said it was "irresponsible and shows the readiness of a powerful elite to continue to drive the Republika Srpska and BiH (Bosnia and Herzegovina) into an ever deeper crisis."
Bosnia became an independent state after the war, but half its population - around two million people - had been displaced, and its infrastructure and economy was left in tatters.
Its political set up is complicated, with the two regions having their own governments, parliament, police and other bodies - linked to a central Bosnian government and rotating presidency.
The country has been encouraged to seek membership of the European Union to strengthen its stability, but it has been unable to escape high levels of corruption, unemployment and political divisions that have put off foreign investors.
President Dodik threatened to hold a referendum on the legitimacy of the central justice system back in 2011 but was held back by pressure from the international community.