Aluminum producer Alcoa said on Tuesday that US President Donald Trump's plan to impose a tariff on aluminum imports could cost about 100 000 US jobs and would itself not be enough to entice it to boost production in the country.

Trump earlier this month said he would impose a flat 25% tariff on aluminum imports "without exceptions or exemptions" in a bid to lift US production of the metal used to make automobiles, cans and other products.

The tariff takes effect on March 4.

Pittsburgh-based Alcoa, which produces aluminum in Canada, Iceland, Australia and elsewhere, had trimmed its output in the United States in recent years partly due to electricity costs.

Bill Oplinger, Alcoa's CEO, told the BMO Global Metals and Mining Conference in Florida that the tariffs could cost about 20,000 US aluminum industry jobs and further 80,000 jobs in sectors that support it.

"This is bad for the aluminum industry in the US. It's bad for American workers," said Oplinger, an engineer by training who became CEO in 2023, in webcast remarks.

US data showed aluminum smelters produced just 670000 metric tons of the metal last year, compared with 3.7-million in 2000. Plant closures in recent years, including in Kentucky and Missouri, have left the country largely reliant on imports.

The tariffs alone would not be enough to entice Alcoa to restart some of its shuttered US facilities, the CEO said, adding that Trump officials have asked the company to do just that.

"It's very hard to make an investment decision, even on something like a restart, without knowing how long the tariffs will last," Oplinger said.

He also said that he has lobbied Trump officials for an exemption on Canadian aluminum imports.

Alcoa would consider boosting US output if it had cheap supply of power, which its Icelandic operations enjoyed, Oplinger said. Aluminum smelting consumes large amounts of electricity.

Separately, Oplinger said he believed that any end to the conflict between Ukraine and Russia could see aluminum from Russia move into Europe.

Oplinger also said he believed there were opportunities for the global aluminum market to consolidate, without providing details.

Shares of Alcoa fell 2.6% to $34.10 in Tuesday morning trading.