In protest of an EU trade agreement with the South American bloc Mercosur that they believe will lead to unfair competition, French farmers drove into Paris on tractors on Thursday. The government issued a warning against "illegal" protests.

In a protest organized by the Rural Confederation union, dozens of tractors came before dawn and cruised through Paris, some arriving at the Arc de Triomphe and others at the Eiffel Tower.

Ludovic Ducloux, co-head of one of the union's chapters, remarked, "We said we'd come up to Paris – here we are."

"No To Mercosur," a reference to the agreement with four South American countries, was written on one of them.

In addition to helping the 27-nation EU export more automobiles, machinery, wines, and spirits to Latin America, the agreement would establish the largest free-trade area in the world.

However, farmers worry that a supply of cheaper goods from Brazil, the world's largest agricultural producer, and its neighbors will undercut them.

Bertrand Venteau, head of the Rural Confederation, told AFP that the farmers planned to peacefully protest at important locations in Paris, even if it meant being detained by the police.

A government spokeswoman on Thursday, however, warned against such “illegal” actions, saying French authorities would “not stand by”.

Blocking a motorway or “attempting to gather in front of the National Assembly with all the symbolism that this entails is once again illegal”, Maud Bregeon told France Info Radio.

In another protest near the southwestern city of Bordeaux, about 40 farm vehicles blocked access to a fuel depot, according to the local authorities.

The government's decision to kill cows in reaction to the rise of nodular dermatitis, a bovine illness often known as lumpy skin disease, has angered farmers in addition to the trade agreement.

President Emmanuel Macron met with farmers at the end of last month to talk about the cull and the trade agreement.

In previous demonstrations, farmers forced the government to reevaluate their policies by blocking highways, spraying manure, and dumping trash in front of official buildings.

In December, some 1,000 tractors were brought into Brussels as part of widespread protests by Belgian farmers against the trade agreement.