Serbian farmers have blocked roads throughout a northern province demanding higher subsidies from the government.
Hundreds of tractors are parked on roads and around towns in Vojvodina province, halting traffic and letting only emergency cars through.
The protests started earlier this week, and have gradually built up.
By Thursday, protesters had closed all roads leading in and out the town of Pancevo, just north of the capital Belgrade. Also closed are other regional roads and a border crossing with Croatia, but not the highway.
Farmers are angry that the government has kept subsidies at about euro140 ($200) per hectare and limited the supported land to 10 hectares (25 acres).