Top White House economic adviser Gary Cohn has said that he is resigning.
The Wall Street banker opposes hefty steel and aluminum tariffs planned by US President Donald Trump.
"It has been an honour to serve my country and enact pro-growth economic policies to benefit the American people, in particular the passage of historic tax reform. I am grateful to the President for giving me this opportunity and wish him and the Administration great success in the future", Mr Cohn said in a statement issued by the White House.
His departure as director of the National Economic Council came after a little more than a year in the job.
Following the news of Mr Cohn's departure, the US dollar weakened, while an exchange-traded fund tracking the broad market S&P 500 dipped 1%.
Mr Trump's announcement last week of his plans to impose the tariffs sent US stock prices tumbling and came after an intense debate within the White House between Mr Cohn and other advocates of free trade, on one side, and protectionist advisers such as Peter Navarro on the other, White House sources said.
Mr Cohn, a former president and chief operating officer of investment bank Goldman Sachs, was seen as a bulwark within the White House against protectionist policies.
Business lobbyists frequently cited him as their strongest ally in the White House.
President Trump said that Mr Cohn had "helped to deliver historic tax cuts and reforms" and he thanked him for his service.
President Trump on the departure of his economic advisor Gary Cohn: "Gary has been my chief economic advisor and did a superb job in driving our agenda, helping to deliver historic tax cuts and reforms... He is a rare talent, and I thank him for his dedicated service..."— Brian O'Donovan (@BrianOD_News) March 6, 2018