THE HAGUE — Thousands of tractors rumbled into The Hague on Wednesday as farmers protested a clampdown on nitrogen emissions that could wreak havoc on their businesses.

“Over the past 20 years, the agricultural sector has moved back and forth along with the rules imposed by politicians,” said Eddy van Wezel, a farmer from Huijbergen, a village close to the Belgian border, who drove by tractor to the Dutch legislative capital with his young son. “Now farmers are forced to bear the brunt of emergency measures to combat nitrogen emissions.”

In May, the highest administrative court in the Netherlands ruled that government laws for granting construction permits and farming activities that emit large amounts of nitrogen are in breach of EU legislation. That forced a halt to up to 18,000 infrastructure and construction projects. Livestock farms are also seen as a crucial way of cutting nitrogen emissions, endangering an important sector of the Dutch economy and enraging farmers.

Wednesday's protest is the third mass demonstration by farmers.

The country's 12 provinces last week adopted new rules on nitrogen emissions. The new rules try to find some wiggle room on emissions by counting the actual number of animals being kept by a farmer, not the often higher number for which they have a permit. The resulting surplus could be transferred to other sectors, like construction companies, which have already exceeded their nitrogen emissions limits.

In the northern province of Groningen, police had to hold back farmers who tried to drive a tractor through the front door of the provincial assembly.

But farmers felt that they are being forced to bear most of the pain, and convoys of tractors converged on eight provincial assemblies on Monday.

In the northern province of Groningen, police had to hold back farmers who tried to drive a tractor through the front door of the provincial assembly. The building was pelted with eggs, and police from Germany were summoned to support their Dutch counterparts.

The legislative united front quickly collapsed. So far, three councils have scrapped the tighter rules, while one province has suspended them.

The central government condemned both the violence, and the decision by the four provincial assemblies to change their rules. The worry is that different rules between provinces will create a regulatory headache.

Other EU countries could soon face the same problems as the Netherlands.

If the rules don't change, the farmers and their tractors will return, warned Micha Bouwer, spokesperson for the Farmers Defense Force.

Nitrogen oxides emissions, which stem mainly from transport, have fallen in recent years thanks to the introduction of emissions controls in cars. Ammonia emissions from farming, however, have steadily increased since 2014. Austria, Croatia, Germany, Ireland, the Netherlands and Spain all reported higher-than-permitted emissions levels in 2017, according to the European Environment Agency.

A European Commission official acknowledged that the management of nitrates pollution is "one of the biggest environmental challenges" for the Netherlands and other EU countries. The Commission is "in touch" with the Dutch authorities following the court ruling, but the official said Brussels is not planning to amend the relevant nature directives.

“It’s a matter of time until there will be similar court case in Germany,” Volkhard Wille, chairman of the conservation group NABU in the Lower Rhine region, said in a phone interview. “If you look at nitrogen emissions in Northwestern Europe, you will see that the values in the Ruhr area and the Lower Rhine do not differ significantly from those in the Netherlands.

But that will only be possible once Germany updates its legislation. Currently German courts use a much higher threshold value for measuring the impact of nitrogen emission impacts than called for by EU legislation.

Dutch farmers want those same looser standards applied to them.

Van Wezel, an organic dairy farmer, said he wants Agriculture Minister Carola Schouten to harmonize rules across the EU. “We’re losing our competitive position to neighboring countries such as Belgium and Germany if they can continue to expand their agricultural sector.”

If the rules don't change, the farmers and their tractors will return, warned Micha Bouwer, spokesperson for the Farmers Defense Force, a militant farmers' organization.

"I want an evaluation within two weeks" of all agricultural legislation, he said. "If not, we will be back."

This article has been updated with a European Commission comment.