Washington DC - President Donald Trump on Sunday threatened to veto legislation to extend federal health insurance subsidies under the Affordable Care Act, raising uncertainty around the cost of healthcare.

Trump told reporters aboard Air Force One that he'd be willing to veto legislation to extend Affordable Care Act (ACA) subsidies if it were to pass the Senate and land on his desk.

"If it passed the Senate, would you veto it or not?" a reporter asked Trump, referring to the ACA. In response, Trump simply said, "I might, yeah."

The remark comes less than a week after 17 Republicans voted alongside Democrats to pass legislation in the House of Representatives that would extend federal subsidies.

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While Republicans defied Trump in voting for an extension in the House, it is widely expected that the bill will be defeated in the Senate.

Legislation to extend the ACA became necessary after subsidies ran out when the clock ticked over into the new year, leaving millions of US citizens facing massive health insurance price hikes.

A potential extension of Obamacare subsidies would see health insurance tax breaks reinstated for a further three years.

The expiration of ACA subsidies on January 1, 2026, saw many household healthcare premiums more than double overnight.

"The affordability crisis is not a hoax. It is very real despite what Donald Trump has had to say," House Minority Leader Hakeem Jeffries told reporters after the bill passed last week.

"Housing costs are too high. Grocery costs are too high. Utility bills are too high. Childcare costs are too high. And healthcare costs are out of control," he said.