Hong Kong student leader Joshua Wong accused HSBC of "political censorship" on Wednesday after the bank rejected his application for a joint account for his new party as well as a personal account for himself.
Wong, 19, announced the formation of the party, called Demosistō, last month to contest parliamentary elections later this year, saying it would push for "self-determination" over the semi-autonomous city's future.
Fears over Beijing's influence have sparked increasing calls, particularly among young activists for more autonomy from the mainland, with some advocating outright independence for Hong Kong.
Both the Hong Kong authorities and Beijing have slammed independence campaigners. One new pro-independence party has said it has been blocked from registering in the city.
Wong, who became the face of the city's pro-democracy movement during mass rallies in 2014, said his application for two accounts with HSBC had been refused with no detailed reason given.
"They may think I'm quite politically sensitive and they need to adopt political censorship," Wong told AFP.
Wong said he applied for a joint personal account with a fellow campaigner to receive donations for his political party, and a personal account for himself -- an upgrade from a children's account that he already had with the bank.
"HSBC phoned us and told us that because of administrative arrangements and business reasons, we are not allowed to open the joint account," said Wong.
"They just continued to repeat to us that it's a business arrangement, sorry about it."
Wong said a second application for his own personal account was also rejected, adding that one branch manager told him he would not be able to open any new accounts at HSBC.
The manager, who Wong said refused to provide a written reason, again told him the decision was due to a "business arrangement," he said.
HSBC told AFP it could not comment on individual cases, but denied there were political reasons at play.
"While we are not commenting on political matters, the bank will not refuse to open an account because of customers' political views," it said.
Hong Kong's freedoms are protected by a 50-year agreement signed when Britain handed the city back to China in 1997, but there are concerns Beijing is weighing in more heavily in a range of areas, from politics to media and education.
HSBC is currently embroiled in the Panama Papers leaks, in which it is named as one of the major international banks most involved in setting up offshore companies for wealthy clients.