Farmers in northern Greece have blocked traffic on the country's main highway, intensifying nationwide protests against budget austerity measures demanded by bailout lenders.

Protest organizers said Tuesday that a tractor blockade on the highway linking Athens to Greece's second largest city, Thessaloniki, would be in effect indefinitely unless the government withdrew proposals for tax hikes and an overhaul of the pension system.

The new austerity measures have prompted broad protests against Prime Minister Alexis Tsipras' year-old leftwing government, with strikes from a broad range of professional groups, from lawyers to ferry workers.

Farmers from across Greece are planning to travel to Athens on Friday, with plans to stage a three-day protest outside parliament.