Brokers and other financial groups from New York to Hong Kong have been left scrambling to comply with a US presidential ban on investment in companies with alleged ties to the Chinese military.

Donald Trump’s executive order, which comes into effect on January 11, days before he leaves the White House, has flummoxed financial institutions, leaving the New York Stock Exchange banning a handful of Chinese companies, reinstating them days later, and on Wednesday banning them again under pressure from the Trump administration. On Thursday concerns over how the blacklist will apply hit shares in US-listed Asian tech stalwarts Alibaba and Tencent.

Lawyers and financial executives say the ambiguously worded rules and guidance over how they will be enforced have sown confusion over how to avoid legal and financial penalties.