American Express warned on Wednesday that US tax changes would hit its bottom line by $2.4bn and plunge it into losses for the fourth quarter.
In a filing American Express said the changes to US law meant earnings per share for the 2017 year would be below its $5.80 to $5.90 guidance range.
However, the company adopted an upbeat outlook, saying a reduction in US corporate tax would bring “significant ongoing benefit”.
President Donald Trump signed US tax reforms into law in December after finally receiving legislative approval amid fierce opposition from Democrats.
Among the provisions, the US top rate of corporation tax falls from 35% to 21%.