Tenex, a Russian state-owned uranium company, is warning American customers that the Kremlin may preemptively bar exports of its nuclear fuel to the US if lawmakers in Washington pass legislation barring imports of it starting in 2028, according to people familiar with the matter.

Tenex’s US subsidiary has warned electric companies including Constellation Energy Corp., Duke Energy Corp. and Dominion Energy Inc. to prepare for such an outcome, one of the people said, adding that the Kremlin has not made a final decision.

Constellation, Duke and Dominion didn’t immediately respond to a request for comment.

Such a move risks wreaking havoc in uranium markets, causing prices to spike for the nuclear reactor fuel that may be harder for smaller utilities to absorb. The outlook for an outright US ban is still unclear. A House-passed measure barring the import of enriched Russian uranium is pending in the Senate.

The impact of a potential Russian move to bar enriched uranium exports to the US is also contingent on the timing. The legislation pending before Congress allows the import of Russian uranium until 2028 through waivers to give utilities time to line up alternative supplies. 

Russia provided almost a quarter of the enriched uranium used to fuel America’s fleet of more than 90 commercial reactors, making it the No. 1 foreign supplier to the US last year, according to Energy Department data.

Without the waivers in the legislation, a 20% increase from the current enrichment spot price of $152 per separative work unit to a record high $180 per SWU is possible, according to Jonathan Hinze, president of nuclear fuel market research firm UxC LLC. Enriched uranium is measured in separative work units, or SWU, which account for the volume and enrichment density of the radioactive metal.

“But if there is an immediate ban it could be even more extreme,” Hinze said. “There are very limited supplies available.”