In a significant setback for Turkey’s opposition, Istanbul University announced on Tuesday that it had revoked the diploma of Ekrem Imamoglu, the leading political challenger to President Recep Tayyip Erdogan. The decision—just days before the opposition was set to nominate him as its presidential candidate—could derail his ambitions in the 2028 elections.

Imamoglu, the mayor of Istanbul and a prominent figure in the Republican People’s Party (CHP), dismissed the university's ruling as illegitimate and beyond its authority.

"This decision is unlawful, and those responsible will be held accountable before history and justice," he declared on X (formerly Twitter). "The people’s march for justice, democracy, and the rule of law will not be stopped."

Istanbul University defended its ruling, stating that 38 individuals, including Imamoglu, had transferred into its English-language Management Faculty in 1990 under irregular circumstances. The school annulled the diplomas of 28 graduates, citing violations of Higher Education Board (YOK) regulations.

The decision could bar Imamoglu from running for president, as Turkish law mandates a university degree for eligibility.

The ruling has intensified concerns over government pressure on opposition figures, with critics calling it part of a broader legal crackdown. Imamoglu has faced multiple indictments, and Erdogan’s administration has increasingly appointed government trustees to replace opposition-held municipal officials.

CHP Chairman Ozgur Ozel condemned the decision as a "dark smear", while IYI Party Chairman Musavat Dervisoglu called it "more than just an attack on a political rival."

Imamoglu’s lawyer had previously told Reuters that his client’s diploma was legitimate, and the university had already ruled in his favor.

Imamoglu, a two-term mayor, has emerged as one of Erdogan’s most outspoken critics, strengthening his political profile in recent months. The CHP and its allies were set to officially nominate him on March 23, despite the diploma controversy.

If the university’s ruling is upheld, Imamoglu would be ineligible to run for president, marking a major victory for Erdogan’s government in its efforts to weaken political challengers.