The boss of US bank JP Morgan Chase has warned British staff that a Brexit could lead to the company making job cuts in the UK and shifting more roles to the rest of Europe.
"A vote to leave would be a terrible deal for the British economy," said the bank's chief executive Jamie Dimon.
"So if the UK leaves the EU, we may have no choice but to reorganise our business model here. Brexit could mean fewer JP Morgan jobs in the UK and more jobs in Europe."
Dimon made the comments at an event also attended by chancellor George Osborne in Bournemouth, where JP Morgan employs 4,000 staff. In total, 16,000 of the bank's workers are based in the UK.
"One realistic outcome is that we lose the ability to passport our banking and trading services into Europe," Dimon added.
"But our clients will still need us to trade within what will then be the EU. If that's what the rules say, we will need to do what works."
Tory MP Steve Baker, who wants Britain to leave the EU, hit back. “The British people will not be bullied into voting to hand more money and more power to Brussels by someone whose bonus would make even some eurocrat’s eyes water and whose bank helped crash the economy,” Baker said.
Dimon has been backing a Remain vote for months now, and in April he warned JP Morgan shareholders that a vote to leave the EU would hurt the UK's economy.
“In a bad scenario, and this is not the worst-case scenario, trade retaliation against Britain by countries in the European Union is possible," he said at the time.
And JP Morgan is among the Wall Street banks to have donated money to the Remain campaign, alongside rivals Morgan Stanley, Citi and Goldman Sachs.
Goldman Sachs and JP Morgan are understood to have pledged £500,000 each, with Morgan Stanley donating around £250,000. Meanwhile, executives at Citi reportedly agreed to donate a sum significantly in excess of £100,000, and possibly as much as £250,000.
The five largest US banks employ 40,000 people in London, which is more than the rest of Europe combined.