Argentine union members and environmentalists protesting the construction of a plant by U.S.-based seed giant Monsanto have clashed.

Local media report they came to blows outside the plant in Cordoba province Thursday.

Environmentalist Vanina Barboza charges in comments to local TV that dozens of workers from the Argentine Construction Union attacked the protest camp near the plant, injuring 20 activists and stealing personal objects.

Monsanto executive Adrian Vilalba accuses the environmentalists of destroying workers' cars.

Construction of the corn-processing plant was halted in October when environmentalists began disrupting entry of supplies. Barboza says they'll continue to block roads and access to the plant.

Workers say the environmentalists are cutting them off from their livelihood.

The state news agency Telam says the violence is being investigated by a local prosecutor.