Australian steel exporters face a wait to find out whether the United States will slap an import quota on local steel and aluminium.
US President Donald Trump has put a May 1 deadline on the tariff exemption he gave Australia and other countries, throwing steel exporters back into uncertainty.
Australia's peak body representing the steel industry says it's too early to tell what the impact will be.
"I don't think until the details come out that we really know what the implications of what he is announcing or is not announcing," Steel Institute chief executive Tony Dixon said on Friday.
The White House said Australia, Europe, South Korea, Canada, Mexico, Argentina and Brazil will initially escape 25 per cent steel and 10 per cent aluminium tariffs.
But the exemption will only last until May 1 "pending discussions of satisfactory long-term alternative means to address the threatened impairment to US national security".
US Trade Representative Robert Lighthizer and Mr Trump's policy adviser Peter Navarro will closely monitor imports of steel and aluminium from Australia and other exempted countries.
"(They) may advise the president to impose quotas as appropriate and further action by the president would be needed to implement any quota," the White House said.
Mr Navarro told CNN the exempted nations would be saddled with steel and aluminium quotas to prevent non-exempted nations attempting to find backdoor entry points to America.
"If you don't put a quota on, then any country that can do whatever they want will become a trans-shipment point for any other country," he said.
He did not specify the likely size of the Australian quota.
Prime Minister Malcolm Turnbull reminded the US it already had "very fair and reciprocal" trade with Australia.
"As they said today, there is no tariffs on US imports into Australia, and it's as fair a trade deal as the US could possibly have," Mr Turnbull told reporters on Friday night.
Australian Industry Group chief executive Innes Willox said it was "deeply disturbing" to see the volatile behaviour from the US.
"Australian business is increasingly concerned by the uncertainty and potential disruption created by these whimsical policy shifts," he said.
