Source: PaxForex Premium Analytics Portal, Fundamental Insight

Shares of aluminum giant Alcoa (NYSE: AA) fell 10.7% in early trading on Wednesday and, although they rose slightly, ended the day with a decline of still large 8.7%. And on the day when the entire S&P 500 fell by 2.6%, mainly due to concerns about the coronavirus, it is not surprising that Alcoa was on the sidelines.

Surprisingly, it happened on the day of good news for Alcoa.
Trump's administration has threatened to revise 10% tariffs on aluminum exports from Canada to the USA, which will raise the cost of imported aluminum and make Alcoa more competitive in terms of price. (Or, conversely, to make it easier for Alcoa to raise price and earn more profit, without having to compete on price).  

You would think that investors would take this as good news for stocks and raise the price. But Alcoa does not want the USA government to set tariffs on Canadian aluminum.
According to Reuters, the Aluminum Association, a trade group representing Alcoa's "blue chip" and other aluminum companies, claims that Canadian aluminum exports have "remained virtually unchanged" over the past three years, and thus do not represent a kind of anti-competitive dumping in the USA market. Unlike China, which, according to Alcoa, overproduces subsidized aluminum and dumps it abroad, CFO William Oplinger says Alcoa wants to compete freely with countries such as Canada, "which are free to trade" with the United States.
In that case, in fact, Alcoa seems to be giving up free money from the US government. This seems strange, given that Alcoa lost money every quarter of last year, and it is expected to lose money both this year and next year (according to analysts gathered by S&P Global Market Intelligence). 

Honestly, it is not known unless Alcoa is actually worried about Canadian competition, but rather fear that the Trump administration is trying to start another trade war and that by taking measures to help Alcoa domestically, it is risking harming Alcoa's international business instead.