Football’s governing body Fifa is investigating the Hong Kong Football Association (HKFA) for a second booing incident, in a match against China.
Fans booed the national anthem Hong Kong shares with China during last week’s World Cup qualifier match.
HKFA was fined by Fifa last month for a similar incident and was warned against further infringements.
The city has seen lingering anti-Beijing sentiment since last year’s mass pro-democracy street protests.
HKFA said in a statement that “disciplinary proceedings” had begun over the 17 November match, where Hong Kong fans booed the Chinese national anthem March of the Volunteers.
Fans also held up placards saying “Boo” and “Hong Kong is not China” on them. Hong Kong, a former British colony, is a special administrative region of China.
HKFA said it appeared to have violated a clause in Fifa’s disciplinary code on the safety of matches, where associations which organise matches must “ensure that law and order are maintained”.
It has been asked to provide a statement and evidence to Fifa by 1 December, and the result of the investigation will be released before the end of that month.
Fifa’s code also states that the home association is liable for attendees’ “improper conduct”, such as “displaying insulting or political slogans in any form, uttering insulting words or sounds”.
Besides the booing, the match took place without any major incident. It ended in a 0-0 draw, damaging China’s prospects in the World Cup, to the delight of Hong Kong fans.
Tensions had been building up before the match, and for the first time Hong Kong and mainland fans had to use separate entrances and bathrooms to prevent clashes.
HKFA was fined 40,000 Hong Kong dollars ($5,160; £3,420) last month when fans booed the Chinese national anthem during a World Cup qualifier match between Hong Kong and Qatar in September.
Fifa had then warned HKFA that “any further infringements will lead to more severe sanctions”.
The association had then blamed the booing on a small minority of fans.