Snowballing protests by French farmers crept closer to Paris on Thursday, with tractors driving in convoys and blocking roads in many regions of the country to ratchet up pressure for government measures to protect the influential agricultural sector from foreign competition, red tape, rising costs and poverty-levels of pay for the worst-off producers.

Traffic-snarling drive-slows, barricades of straw bales, stinky dumps of agricultural waste outside government offices, and other demonstrations have rapidly blown up to become the first major crisis for newly appointed Prime Minister Gabriel Attal, installed two weeks ago by President Macron in hopes of injecting new vigor into his administration.

Mr. Macron’s opponents are seizing on the farmers’ demonstrations to bash his government’s record ahead of European elections in June. Rightist leader Marine Le Pen, whose National Rally party is polling strongly, blamed free-trade agreements, imports and bureaucracy for farmers’ economic woes.

“The worst enemies of farmers are to be found in this government,” she said Thursday.

Roads hit Thursday morning by drive-slows included a highway west of the French capital and seat of power. “We are getting progressively closer to Paris,” farmer David Lavenant said to broadcaster BFM-TV.

BFM-TV images from Agen, in southwest France, showed a supermarket being showered with a thick jet of pig slurry. There were roadblocks and other demonstrations elsewhere.

In Brussels, the EU Commission president, Ursula von der Leyen, opened a discussion panel to try to put farming on a new footing, hoping to take into account some of the complaints raised by protesters around the 27-nation bloc.

The so-called strategic dialogue comes as campaigning for the June 6 to 9 EU parliamentary elections is picking up steam and the fate of the farm sector is expected to be a hot-button issue.

“We all agree that the challenges are, without any question, mounting, said Ms. von der Leyen, be it “competition from abroad, be it overregulation at home, be it climate change, or the loss of biodiversity, or be a demographic decline, just to name a few of the challenges.

In recent weeks, farmers have staged protests in Germany, the Netherlands, Poland, and Romania.