Copper prices have been on a tear recently and the rally was starting to look unstoppable.

But copper futures tumbled, along with mining stocks, ahead of the open Thursday as a key element of the rally was thrown into doubt-the White House is hesitating over a decision on tariffs on refined copper products, Reuters reported.

Officials are weighing up the issue of higher prices increasing manufacturing costs against the benefits of encouraging domestic mining, it said, citing two people familiar with the matter.

The likelihood of tariffs being imposed was a major factor in copper prices surging to record highs earlier this week. Insatiable demand for artificial-intelligence infrastructure has been another catalyst-the metal has become critical in the data-center buildout. It's also crucial for power grids and electric vehicles.

Continuous copper futures fell 4.7% to $6.56 per pound early in the day, after settling at a record high of $6.89 in the previous session. Copper prices are still up more than 15% in 2026.

It looks set to be a bad day for copper mining giant Freeport-McMoRan. The stock, which is up more than 50% this year through Wednesday's close, was pointing 8% lower ahead of the open Thursday.

Brazilian miner Vale's American depositary receipts slipped 3.6% in premarket trading, while London-listed miners Antofagasta and Anglo American were both down close to 6%. Glencore, Rio Tinto, and Fresnillo also fell as the U.K.'s blue-chip FTSE 100 index slipped 0.6%.

But the fall in prices may help ease the pressure on industrial companies. Mizuho analysts said in a note Wednesday that copper futures trading near all-time highs "implies annualized operating-profit headwinds," for 3 HVAC (heating, ventilation, and air conditioning) stocks-Trane Technologies, Lennox International, and Carrier Global.