Us President Donald Trump suggested in announcing the move on Twitter that he was acting because he’s not satisfied with the pace of progress in negotiations with China.

Tariffs on $200 billion of Chinese imports will increase to 25 percent from 10 percent on Friday, and another $325 billion in goods will “shortly” be subject to tariffs, President Donald Trump said Sunday, in a warning to China as what could be a closing round of talks for a trade deal are set to start in Washington this week.

….of additional goods sent to us by China remain untaxed, but will be shortly, at a rate of 25%. The Tariffs paid to the USA have had little impact on product cost, mostly borne by China. The Trade Deal with China continues, but too slowly, as they attempt to renegotiate. No!

— Donald J. Trump (@realDonaldTrump) May 5, 2019