DIYARBAKIR, Turkey — As the June 24 presidential and parliamentary polls approach, Turkey’s opposition parties are concerned about possible foul play in the critical race, which is looming as the toughest election battle for the government yet.

The polls will mark Turkey’s transition to a super-presidency system tailor-made for President Recep Tayyip Erdogan, whose victory, many fear, would seal the demise of Turkish democracy, making election integrity all the more critical. The new system was narrowly approved in a controversial referendum last year. International observers said at the time that up to 2.5 million votes — almost double the winning margin of the “yes” vote — might have been manipulated, as the Higher Electoral Board (YSK) made a last-minute decision to validate ballots unstamped by election officials.

The YSK’s decision and subsequent changes to election rules in March have stoked misgivings over the fairness of the upcoming polls, in which small margins could be of big significance.

In a move that further fueled concerns, the YSK said May 28 it had decided to relocate polling stations in predominantly Kurdish areas that would affect 144,000 voters, citing security reasons. The move, made possible by the March amendments, infuriated the pro-Kurdish Peoples’ Democratic Party (HDP), which claims the authorities are maneuvering to push the party below the 10% threshold required to enter parliament.