On Friday, the shadow Business Secretary said that more companies might consider moving their headquarters away if the Conservatives were voted back into power.
"I do not believe this will be the only... large institution we see listed here in London making these kinds of statements at their AGMs. I think if we see the Conservatives continue in office they are all going to have to make statements about this," Labour's Chuka Umunna told CNBC on Friday.
"This is really quite significant, because here you have one of the biggest banks in the world saying that if the U.K. leaves EU that will be significant adverse event," he added later.
While other business leaders have express concerns about Britain's uncertain future in the EU, the U.K. bank levy—which HSBC paid around £750 million towards last year—is also believed to be a large factor in HSBC's considerations.
On Friday, Hargreaves Lansdown, a FTSE 100-listed investment management firm, said that the bank levy had reduced the value of U.K. bank shares by around £25 billion ($38 billion) since its introduction.
Analysts at Bernstein said a move to Hong Kong would "make total sense" for HSBC and said that U.K. rival Standard Chartered was likely to follow suit.
"We think the move to Hong Kong (obviously) makes total sense. Releases almost $14 billion in value; is a move that has already been welcomed by KHAM and one that can be done at minimal cost," Bernstein said in a research note on Friday.
Also on Friday, the Institute of Directors warned that other U.K. stalwarts might look to relocate.
"From uncertainty over the U.K.'s relationship with Europe, to the threat of higher taxes on companies and individuals, nobody can be surprised that major international organisations keep their relationship with the UK under review," said Simon Walker, director general of the U.K. business lobbying group, in a statement.
"This warning from one of the U.K.'s biggest companies should force politicians to pay heed to the effects of both their policies and their rhetoric, and to take seriously the threat of a major withdrawal from the British economy."
Bernstein added that a relocation by HSBC could increase the bank levy burden on its competitors remaining in the U.K.
"Recouping the loss from the likes of Lloyds, RBS and Barclays could see their levy increase 70 percent," the analysts said.