Iran has a long history of trying to control what its citizens can and can't see on the web. From blocking Google searches and all foreign email providers, to cutting access to social networks services and even announcing plans of creating its own domestic "Internet" -- an intranet which would be isolated from the rest of the world. Those more technically inclined have been able to bypass these state-sponsored filters for a while using proxy servers and virtual private networks, but now it seems authorities are tightening their grip.
According to Reuters, Iranian authorities have blocked the use of most “illegal” VPN services in the last few days. Ramezanali Sobhani-Fard, the head of parliament’s information and communications technology committee, explained that “only legal and registered VPNs can from now on be used.” As you'd expect, those sanctioned VPNs are subject to surveillance and adhere to the official website blocks.
The latest crackdown comes just a few months ahead of a presidential election scheduled for June, its first since 2009. Back then Iranians protested election results en masse, leading to the worst unrest since the 1979 Islamic revolution. Protesters used services like Facebook to communicate during those "Green Movement" demonstrations and apparently the government is determined to prevent a repeat this time.
Government officials had previously said that Iran’s domestic intranet would be ready by this month, which could also mean the VPN ban is a precursor to a wider rollout of the new system.
Sobhani-Fard noted that the government's move to block VPN access may also have inadvertently cut off access to widely used sites such as Yahoo and Google, adding that parliament will study the issue this week.