Lloyds Banking Group has warned that a Brexit would create "economic uncertainty" in the short-term.
Tentatively throwing its weight into the crucial debate, the bank, which is still part-owned by the taxpayer, said it was "unclear" what the long-term impact of a Brexit would be.
In a statement, Lloyds Banking Group said: "The board is mindful that the future of the UK's relationship with the EU is a matter for the UK electorate, and that for many the debate is about more than just economics."
"Warts and all"
Earlier in the day, Labour leader Jeremy Corbyn made his first big speech on the EU referendum.
He told Labour supports in London that while he has criticised the Union in the past, he believes change can only be achieved as part of it. He warned that the UK faces a "bonfire" of workers' rights if a Conservative government was allowed to rule without EU oversight.