City A.M. understands that the dinner is being held in central London this evening to bolster the coffers of campaigners who are vying to keep Britain in the European Union, and foster closer links with the financial sector.
Britain Stronger in Europe is chaired by former M&S boss Lord Rose, while its treasurer is Roland Rudd, head of top City PR firm Finsbury.
Key City figures were invited to the fundraiser, where tables are understood to have been available for five-figure sums.
Several banking giants have already contributed generously to the Remain campaign. Goldman Sachs and JP Morgan are understood to have pledged £500,000 each, while Morgan Stanley has pledged nearly £250,000.
Citigroup became the latest US bank to give to the campaign last week with a six-figure sum.
When asked about the top-dollar bash, a Britain Stronger in Europe spokesperson told City A.M. that they would "not provide a running commentary" on fundraising matters.