Serbia's populist leader Aleksandar Vucic faces a key parliamentary election this weekend. His allies in Bosnia are helping by banning rallies supporting a Serbian student movement challenging him.

LJILJANA SMILJANIC BANJA LUKA, Bosnia-Herzegovina — With Serbia’s populist leader Aleksandar Vucic facing a key parliamentary election this weekend, his allies in neighboring Bosnia are doing everything they can to help — including banning rallies in support of a Serbian student movement that is Vucic’s main challenger in the vote.

Bosnia has a large ethnic Serb population with thousands of dual nationals with both Bosnian and Serbian citizenship, thanks to historic and ethnic ties stemming from the era of the joint Yugoslav federation. They are eligible to vote in Serbia’s election and are part of that country’s 6.4-million-strong electorate.

The leaders of Bosnia’s autonomous ethnic Serbian republic — known as Republika Srpska — are close allies of Vucic, but many ordinary people are also sympathetic to the student protesters who have challenged Vucic’s tight grip on power in Serbia.

In the past month, Bosnian Serb police banned two events that students in Republika Srpska tried to organize in support of their fellow students in Serbia. Police cited security reasons for the latest ban of a student gathering in the northwestern town of Banja Luka on Monday.

Students in Banja Luka insisted the decision was political, saying the local authorities “don’t want to allow an image of unity with our colleagues in Serbia to be shown.”

The informal group “Students for students” said it would take legal action against authorities while Bosnian Serb opposition politician Nebojsa Vukanovic told reporters at a square in Banja Luka where the rally had been planned that the ban was a “disgrace.”Tensions ahead of the vote on Sunday in Serbia are high as Vucic’s Serbian Progressive Party, or SNS, seeks to cling on to power despite widespread popular discontent. Serbia’s students and their Students’ List ticket are believed to be polling close with Vucic’s SNS. Bosnia some 19,800 voters can cast ballots at 28 polling stations throughout the country on Sunday.

Opposition activists and independent monitors in Serbia have in the past accused Bosnian Serb strongman Milorad Dodik and Vucic of organizing mass voting by Bosnian Serbs with dual citizenship to help swing the vote in favor of Vucic, which they have denied.

However, mainstream media in Republika Srpska have only covered the activities of Vucic and his SNS. Dodik routinely attends the party events in Serbia where he also votes, and owns a house. He and Vucic say their good relations are a vehicle for bringing the Serb communities in the two countries closer together.

Republika Srpska makes up about one half of Bosnia while the other half is controlled by the country’s Bosniaks, who are mainly Muslims and Croats. The two entities were formed in a U.S.-brokered peace agreement that ended Bosnia’s 1992-95 ethnic war that killed over 100,000 people and displaced millions.

Dodik has repeatedly called for the separation of the Bosnian Serb entity and its unification with Serbia, a call that has triggered fears of a revival of war-time ethnic tensions. During the war, Serbia backed the Bosnian Serbs in their war against Bosniaks and Croats.

Both Dodik and Vucic have close ties to Russian President Vladimir Putin Bosnia and Serbia are formally seeking European Union membership but efforts have stalled over lack of democratic reforms.