Ukraine’s farmers played an iconic role in the first weeks of Russia’s invasion, towing away abandoned enemy tanks with their tractors.

Now, though, their prodigious grain output is causing some of Ukraine’s staunchest allies to waver, as disrupted shipments are redirected onto neighboring markets.

The most striking is Poland, which has played a leading role so far in supporting Ukraine, acting as the main transit hub for Western weaponry and sending plenty of its own. But grain shipments in the other direction have irked Polish farmers who are being undercut — just months before a national election where the rural vote will be crucial.

Diplomats are floundering. After a planned Friday meeting between the Polish and Ukrainian agriculture ministers was postponed, the Polish government on Saturday announced a ban on imports of farm products from Ukraine. Hungary late Saturday said it would do the same.

Ukraine is among the world’s top exporters of wheat and other grains, which are ordinarily shipped to markets as distant as Egypt and Pakistan. Russia’s invasion last year disrupted the main Black Sea export route, and a United Nations-brokered deal to lift the blockade has been only partially effective. In consequence, Ukrainian produce has been diverted to bordering EU countries: Hungary, Poland, Romania and Slovakia.

At first, those governments supported EU plans to shift the surplus grain. But instead of transiting seamlessly onto global markets, the supply glut has depressed prices in Europe. Farmers have risen up in protest, and Polish Agriculture Minister Henryk Kowalczyk was forced out earlier this month.

Now, governments’ focus has shifted to restricting Ukrainian imports to protect their own markets. After hosting Ukrainian President Volodymyr Zelenskyy in Warsaw in early April, Polish President Andrzej Duda said resolving the import glut was “a matter of introducing additional restrictions.”

The following day, Poland suspended imports of Ukrainian grain, saying the idea had come from Kyiv. On Saturday, Polish Prime Minister Mateusz Morawiecki, after an emergency cabinet meeting, said the import ban would cover grain and certain other farm products and would include products intended for other countries. A few hours later, the Hungarian government announced similar measures. Both countries said the bans would last until the end of June.

The European Commission is seeking further information on the import restrictions from Warsaw and Budapest “to be able to assess the measures,” according to a statement on Sunday. “Trade policy is of EU exclusive competence and, therefore, unilateral actions are not acceptable,” it said.

While the EU’s free-trade agreement with Ukraine prevents governments from introducing tariffs, they still have plenty of tools available to disrupt shipments.

Neighboring countries and nearby Bulgaria have stepped up sanitary checks on Ukrainian grain, arguing they are doing so to protect the health of their own citizens. They have also requested financial support from Brussels and have already received more than €50 million from the EU’s agricultural crisis reserve, with more money on the way.

Restrictions could do further harm to Ukraine’s battered economy, and by extension its war effort. The economy has shrunk by 29.1 percent since the invasion, according to statistics released this month, and agricultural exports are an important source of revenue.

Cracks in the alliance

The trade tensions sit at odds with these countries’ political position on Ukraine, which — with the exception of Hungary — has been strongly supportive. Poland has taken in millions of Ukrainian refugees, while weapons and ammunition flow in the opposite direction; Romania has helped transport millions of tons of Ukrainian corn and wheat.

Some Western European governments, which had to be goaded by Poland and others into sending heavy weaponry to Kyiv, are quick to point out the change in direction.

“Curious to see that some of these countries are [always] asking for more on sanctions, more on ammunition, etc. But when it affects them, they turn to Brussels begging for financial support,” said one diplomat from a Western country, speaking on condition of anonymity.

Some EU countries also oppose the import restrictions for economic reasons. For instance, Spain and the Netherlands are some of the biggest recipients of Ukrainian grain, which they use to supply their livestock industries.

Politically, though, the Central and Eastern European governments have limited room for maneuver. Poland and Slovakia are both heading into general elections later this year. Bulgaria has had a caretaker government since last year. Romania’s agriculture minister has faced calls to resign, including from a compatriot former EU agriculture commissioner.

And farmers are a strong constituency. Poland’s right-wing Law & Justice (PiS) party won the last general election in 2019 thanks in large part to rural voters. The Ukrainian grain issue has already cost a Polish agriculture minister his job; the government as a whole will have to tread carefully to avoid the same fate.

This article has been updated.