The action is part of President Donald Trump's aggressive defense of US trade interests, with anti-dumping and countervailing duty actions up 61 percent since he took office, according to the Commerce Department.
Following a complaint from California producers, the agency found Spanish exporters benefited from impermissible subsidies of between 2.3 and 7.2 percent.
US customs agents will collect cash deposits on olive imports based on those rates, according to the Commerce Department.
In 2016, the US imported an estimated $70.9 million worth of ripe Spanish olives, principally from producers in Seville.
"We will continue to review all information related to this preliminary determination while standing up for American workers and companies," Commerce Secretary Wilbur Ross said in a statement.
A final decision in the case is due in May. The Commerce Department maintains 412 anti-dumping and countervailing duty orders to protect American companies from trade practices Washington deems to be unfair.
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