(Bloomberg) -- Poland’s ruling party pushed through legislation to set up an inquiry panel that could target opposition leader Donald Tusk, kicking off a charged political fight five months before a tightly contested election. 

The investigative committee, approved in a parliamentary vote Friday, would aim to probe Russia’s influence in Poland between 2007 and 2022. Jaroslaw Kaczynski, the powerful leader of the nationalist Law & Justice party, has for years accused Tusk of tolerating Russian influence during his tenure as prime minister before 2015. 

The move places that battle front and center amid campaigning ahead of the vote slated for October, in which the ruling party risks losing its grip on power. Critics have leveled sharp criticism at the panel, calling it a violation of the constitution that would seek to manipulate the contest. 

Poland’s president, Andrzej Duda, must sign it into law for it to take effect. The head of state, who’s built a track record for occasionally vetoing legislation from his own party that he considers to be toxic, hasn’t signaled whether he’ll approve it. 

The committee would have unprecedented powers, with the ability to effectively ban officials from pursuing public office. Parliamentary lawyers have attacked it as a violation of European Union law, while the body’s ombudsman for human rights said parts of it violate the constitution. 

But the prospect of Tusk, the former president of the European Council, being publicly grilled over the Russia accusations while campaigning to oust the ruling party has raised hackles among opposition figures, who say it amounts to a political witch hunt. 

“This is a plan for a dirty election campaign against Donald Tusk and the opposition,” said Tomasz Siemoniak, the deputy chairman of Civic Platform, Tusk’s party. “The ruling party has been in charge for eight years and until now has not been able to carry out any investigation.” 

Kaczynski’s grievance has been a feature of Poland’s politics for well over a decade, tracing its origin to the 2010 plane crash that killed Kaczynski’s twin brother Lech — Poland’s president at the time — and 95 others, including a swathe of the country’s elite. 

Law & Justice’s leader has promoted the circumstances of the crash into a theory widely believed by his supporters that effectively blames then-Premier Tusk for the tragedy through administrative errors.

Independent investigators have attributed the crash in the western Russian city of Smolensk to pilot error during a landing in dense fog. 

Tusk was summoned three times during his tenure in Brussels to answer questions in investigations linked to the crash, and subjected to hours-long testimony. One probe looked into contacts between Poland’s military counterintelligence and Russia’s Federal Security Service. 

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