Top White House economic adviser Gary Cohn is resigning after disagreeing with President Donald Trump's plans to impose new tariffs.
The former Wall Street banker became a key architect of the 2017 tax overhaul and a bulwark against protectionist forces within the Trump administration.
In a statement released by the White House, Mr Cohn said it had been an honour to "enact pro-growth economic policies to benefit the American people" such as 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's resignation came after Mr Trump said he would impose hefty tariffs on steel and aluminium imports in a move that would hit close allies Canada and Mexico.
Mr Trump's pledge to impose tariffs had prompted speculation Cohn might leave the White House because of his opposition to the policy.
Mr Cohn - a former president and chief operating officer of investment bank Goldman Sachs - was one of a number of Wall Street veterans tapped by Trump for senior jobs after the 2016 presidential election.