U.S. wholesale inflation surged unexpectedly last month, signaling that President Donald Trump’s sweeping taxes on imports are pushing costs up and that higher prices for consumers may be on the way.

The Labor Department reported Thursday that its producer price index — which measures inflation before it hits consumers– rose 0.9% last month from June, biggest jump in more than three years. Compared with a year earlier, wholesale prices rose 3.3%.

The numbers were much higher than economists had expected.

Prices rose faster for producers than consumers last month, suggesting that U.S. importers may, for now, be eating the cost of Trump’s tariffs rather than passing them on to customers.

That may not last.

“It will only be a matter of time before producers pass their higher tariff-related costs onto the backs of inflation-weary consumers,” wrote Christopher Rupkey, chief economist at fwdbonds, a financial markets research firm.

Excluding volatile food and energy prices, so-called core producer prices rose 0.9% from June, biggest month-over-month jump since March 2022. Compared with a year ago, core wholesale prices rose 3.7% after posting a 2.6% year-over-year jump in June.

Wholesale food prices rose 1.4% from June, led by a 38.9% surge in vegetable prices. The price of home electronic equipment gained 5% from June. Both are heavily imported in the U.S.

But some aspects of Thursday’s producer price report were puzzling, including a big jump in profit margins at retailers and wholesalers. Economist Stephen Brown at Capital Economics found the increase “to put it lightly, counterintuitive given the anecdotal evidence that firms are absorbing the lion’s share of tariff increases in margins.”

Trump’s tariffs have generated considerable uncertainty about the U.S. economy, the world’s largest, which could explain some seemingly contradictory trends. Trump has negotiated trade agreements with several major U.S. trading partners, including the European Union and Japan. But the details have not been published, leaving businesses uncertain about where tariff rates will end up and therefore whether and how they should adjust their own prices.