Fears over the integrity of Turkey’s upcoming elections have flared anew after the authorities restricted internet access for long hours following the deadly Nov. 13 bombing in Istanbul.

Few legal safeguards exist to prevent internet throttling on election day, IT specialists say, noting that the opposition should have contingency measures in place.

Shortly after the blast, the judiciary imposed a ban on broadcasting from the scene. The Information Technologies and Communication Agency (BTK) followed up with bandwidth throttling in the evening, paralyzing internet access across the country. Millions struggled to access social media networks up until the next morning, and many said they were unable to reach any websites at all. VPN use provided only partial relief in accessing popular platforms such as YouTube, Twitter and Instagram. According to international monitors, demand for VPN services in Turkey surged 853% compared to the daily average over the previous 30 days.

Opposition parties, mounting their strongest challenge yet to President Recep Tayyip Erdogan’s two-decade rule, fear similar restrictions on election day, due in June at the latest. Releases of vote counts have been disrupted in close races in the past. Opposition parties rely on online communication to speedily collect their own data from polling stations and crosscheck the official results. The main opposition Republican People’s Party (CHP) announced last week that it has developed its own VPN application.