The mayors of three Turkish cities were arrested Saturday morning, according to media reports, as Turkey’s President Recep Tayyip Erdoğan continues his crackdown on the political opposition.

All three of the mayors belong to Turkey’s main opposition party, the Republican People’s Party (CHP).

Abdurrahman Tutdere, Zeydan Karalar, and Muhittin Bocek were arrested as part of investigations launched by the public prosecutor’s office in Istanbul, Turkish state-run media reported. They are the mayors of Adiyaman, Adana municipality and Antalya, respectively.

Their arrests come four months after the mayor of Istanbul, Ekrem İmamoğlu, was jailed over allegations of corruption.

İmamoğlu is considered to be the main political opponent to Erdoğan. His arrest in March led to widespread protests, and he was later named as his party’s presidential candidate. The next presidential election in Turkey is due in 2028.

Other CHP figures also have been targeted. The former mayor of Izmir, Turkey’s third-largest city, was arrested along with 137 officials earlier this week on fraud and tender-rigging allegations, the Associated Press reported. State-run media reported that the mayor of Manavgat, also belonging to CHP, was detained with 34 others over corruption allegations.