"These in themselves probably won't upset the apple cart, but it's what happens politically around it," Lewandoski said.
"The biggest concern is how does this escalate? And then does it ultimately impact the global economy? If we go into another 2009 environment, it would really pause investments."
Nick Vafiadis, vice president of plasticts at IHS Markit, notes that China singled out only one of three main types of polyethylene: a low-density category commonly used in packaging, which is fairly well supplied in China.
Still, there is more than a million metric tons of new low-density U.S. polyethylene capacity coming online through next year, most of which is for export, particularly to China, he said. Dow Chemical is ramping up a new facility now, while Formosa and Sasol have plants coming online soon.
Many parts of the U.S. chemicals industry are set up to meet domestic demand, but Chinese tariffs raise questions about the ability of American companies to sell their surplus products on the international market, said Kathy Hall, executive editor of PetroChem Wire.
"If you're stemming the overflow from the get-go, it's a little bit questionable about how that plays out for these news plants," she said, referring to new plastics and petrochemical facilities.
Another question is whether tariffs would affect American firms that have long-term contracts with Chinese partners.
"For companies that are very dependent on China, that have decadelong contract agreements, is that affected by this? I don't know. I wouldn't think so, but I don't know," she said.