(Bloomberg) -- A top aide of Serbian President Aleksandar Vucic requested an investigation into his boss and his brother in a bid to clear them from opposition-led allegations that they’re linked to an illegal marijuana farm.

Opposition parties are struggling to make a dent in the dominant position of Vucic’s ruling Serbian Progressive Party as the Balkan state heads into general elections next spring. His opponents have led sporadic street rallies over the last year to protest against what they say is an autocratic style of governing that stifles media freedom and opens deals to businessmen allies.

The new allegations follow last month’s seizure of almost 4 tons of greenhouse-cultivated marijuana at an organic farm near the capital. Police arrested the owner, who had sought state subsidies for growing non-psychoactive hemp. While there’s no clear evidence that he got financial support, activists accused Vucic and his brother of protecting the farmer.

“There can be only one truth,” Milos Vucevic, the vice president of Vucic’s party, told reporters in Belgrade Monday after filing a request to prosecutors. The aim is to knock down “heinous lies and slander and to establish if those who made the accusations actually lied,” he said.

Opinion polls show Vucic, who started his political career serving under late strongman Slobodan Milosevic, is by far the country’s most popular politician. Opposition parties say that he has unfairly used his position to harness state media to amplify his messages and marginalize his rivals.

“The whole point is to show who’s lying,” Vucic told private Pink TV on Sunday. “You just have to stop that and show people what what kind of liars these people are.”

To contact the reporter on this story: Misha Savic in Belgrade at msavic2@bloomberg.net

To contact the editors responsible for this story: Irina Vilcu at isavu@bloomberg.net, Michael Winfrey, Andrea Dudik

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