"As we continue to look for different ways to enhance our workplace, we’ve decided to expand the business casual dress code firmwide, starting tomorrow," the US bank said, adding that the new dress code "reflects how the way we work is changing".
"More clients are dressing informally, and many parts of our company are already business casual," JP Morgan said in a memo to staff.
The bank reminded employees not to go too far with their new, more relaxed style: "It’s critical that we still maintain a highly professional environment. We trust that all of you will use good judgment in what you wear depending on your roles and daily activities.
"Business casual is not weekend casual, and if you’re seeing a client, you should dress for that client.”
Staff were also referred to the JP Morgan firmwide dress code FAQs and told to go to their managers with any questions about the new rules.
Read more: The new rules of business dress
JP Morgan is not the first bank to give staff more freedom with their apparel choices. Barclays previously brought in a more dressed down look, but was subsequently forced to be more specific with staff about what was acceptable - it banned jeans and flip-flops at its head office last year.
Earlier today, JP Morgan boss Jamie Dimon made a splash when he warned that a Brexit could lead to jobs being cut at the bank in the UK and moved to other locations in the rest of Europe.
"If the UK leaves the EU, we may have no choice but to reorganise our business model here," he said. Brexit could mean fewer JP Morgan jobs in the UK and more jobs in Europe."
Dimon's remarks prompted a blistering response from Tory MP Steve Baker, who said: "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."