Russia’s invasion of Ukraine showed the first signs of stifling trade in vital raw materials, as the money that lubricates the flow of everything from crude oil to wheat began to dry up.

Some European banks have begun to impose restrictions on commodity-trade finance linked to Russia, heaping pressure on traders who were already on the lookout for additional credit and bracing for harsh western sanctions on Moscow.

Dutch banking giant ING Groep NV is restricting lending to commodities deals coming from Russia and Ukraine, said people familiar with the matter. Other European banks are also scaling back their exposure, with some restricting the issuance of letters of credit against cargoes that originated in Russia, people said, asking not to be named because the information isn’t public.

“In the long term, I think things could become much more challenging,” Jean-Francois Lambert, a former commodity banker and now an industry consultant with Lambert Commodities, said by phone. “The cogs are gradually turning, banks will not want exposure and I expect eventually it will be extremely difficult to buy anything from Russia or sell anything there.”

For decades, the commodities-trading industry has relied up hundreds of billions of dollars of short-term financing from international banks. Any disruption to that flow of money would soon be felt in the movement of cargoes of energy, metals and agricultural products around the world.

When Russia launched a barrage of missile attacks on Ukraine early on Thursday, it triggered the worst security crisis Europe has witnessed in decades. U.S. and European leaders haven’t said yet whether they will punish Moscow with sanctions on its major exports, which in addition to oil and gas also include aluminum and wheat, but the crisis is already having a chilling effect.

Russia’s flagship crude oil was offered for sale at a record discount as some buyers and shipping companies pulled back. Some shipments of food and metals were left stranded by the closing of ports and railways in Ukraine.

A financing squeeze would come at the worst possible time for an industry that’s already dealing with historically high and volatile commodity prices. Last year, major energy traders were forced to reduce the size of their positions and increase borrowing to cover margin calls that stemmed from a massive surge in the cost of natural gas.

Sanctions could have a particularly acute impact now because Russian banks have expanded their presence in commodity-trade finance in the last few years. They stepped up to provide additional credit to European trading houses after industry mainstays like ABN AMRO and BNP Paribas announced they’d be leaving commodities.

There are growing fears that these new Russian players, notably VTB, Sberbank and Gazprombank, could be hit with sanctions, forcing traders reliant on them for credit lines to look elsewhere, several sources with direct knowledge of the matter said.

A Biden administration official told reporters on Tuesday that the U.S. administration was prepared to sanction VTB and Sberbank, Russia’s two biggest banks, as part of a potential response to an escalation of hostilities in Ukraine. On Thursday, U.K. Prime minister Boris Johnson unveiled a tough package of penalties including an asset freeze against all major Russian banks.

ING, one of the largest financiers to the commodities industry, is also curbing lending to some Russian and Ukrainian clients, the people said. The bank is still considering financing for some clients on specific commodity flows on a case by case basis, one person said.

A spokesman for ING didn’t immediately return a call seeking comment.