China’s foreign ministry and embassy urged citizens traveling to the United States to avoid Seattle-Tacoma International Airport on Thursday, citing what Chinese officials described as a pattern of continual harassment by U.S. Customs and Border Protection personnel. The advisory followed the denial of entry to about 20 Chinese scholars who arrived at the airport with valid visas to attend an academic conference.

China Consular Affairs said in a post on X that the academics were “unreasonably inspected” by CBP personnel before being refused entry. Spokespersons for CBP, the Chinese Embassy in Washington, D.C., and its consulate in San Francisco had not responded to requests for comment as of Thursday.

The foreign ministry told travelers to familiarize themselves with U.S. entry regulations before any trip. “If you encounter questioning from U.S. enforcement personnel, you should deal with it calmly and rationally,” the ministry said, according to a translation of the post.

Seattle ranked as the sixth largest metropolitan area in the country for Chinese population in 2019, with about 166,000 residents, according to Pew Research Center.