Stocks closed sharply lower Friday after the US threatened to impose tariffs on goods from Mexico, potentially opening a new trade war front.

The Friday slump is emblematic of the month of May for stocks. The Dow Jones Industrial Average fell 1.4% while the S&P 500 slumped 1.3%. The Nasdaq Composite Index surrendered 1.5%. The major market indexes all closed May with sharp losses and closed the shortened trading week lower.

Trade issues were again at the forefront of the market’s attention Friday. President Donald Trump on Thursday said in a tweet that the US will place a 5% tariff on goods from Mexico “until such time as illegal migrants coming through Mexico, and into our Country, STOP.” Trump said the tariffs will rise until the immigration situation “is remedied.”

Major market indexes plunged in May. The Dow fell 6.7% while the S&P 500 slumped 6.6%. The Nasdaq tumbled 7.9%. For the week, the Dow fell 3%, the S&P 500 slumped 2.6% and the Nasdaq tumbled 2.4%.

Much of the decline this month for stocks has been blamed on the renewed trade tensions between the US and China. As the trade dispute has dragged on, concerns have mounted over economic growth.

On Friday communications services was the biggest losing sector in the S&P 500, plunging 2% followed by energy, which fell 1.6% as oil prices tumbled again. West Texas Intermediate crude oil futures swooned 5.9% to $53.26 per barrel in late trading. Technology stocks fell 1.6%.

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