Most U.S. factories in China’s manufacturing hub around Shanghai will be back at work this week, but the “severe” shortage of workers due to the coronavirus will hit production and global supply chains, according to the American Chamber of Commerce in Shanghai.

While about 90% of the 109 U.S. manufacturers in the Yangtze River delta expect to resume production this week, 78% of them said they don’t have sufficient staff to run at full speed, according to a survey by AmCham. The biggest reasons for that were travel restrictions on their staff returning from holidays and the requirement to quarantine them for two weeks once they do come back.

“Most factories have a severe shortage of workers, even after they are allowed to open,” Chamber President Ker Gibbs said in an email. “This is going to have a severe impact on global supply chains that is only beginning to show up.”

Almost 60% of the firms expect demand to be lower than normal over the next few months, nearly half said their global supply chain had already been affected by the business shutdown, and about a third of them will consider moving operations out of the country if this continues, according to the survey.