The owners of a coffee shop in the American state of Indianapolis were shocked after a couple decided to have their wedding there without any warning.

Mansion Society in the town of Hawthorne ended up swarming with a full bridal party alongside regular patrons on New Year’s Eve, People reported.

The wedding party and guests walked in and proceeded to leave personal items and wedding gifts throughout the shop, while the ceremony then took place during regular service.

The group of about 20 to 30 people took pictures and video, blocking the entrance and asking staff to watch over their belongings.

In a post on Instagram, the Mission Society asked patrons to be considerate and book in advance if they want to host an event at the venue.

Since posting about the incident, a GoFundMe page has been set up and donations have been flowing in to the shop.

The bride in question has also reached out to the owners and offered them a US$200 (NZ$319) donation as compensation for the hassle caused.

The Mansion Society has written a letter to the married couple asking them to pay the US$500 they charge for a regular wedding booking along with some harsh words about what went down.

“Without asking, consideration and zero care to those patrons around you or us, you proceeded to have a wedding with a group of at least 20 people,” the owners said in their letter.

They added “your ‘donation’” doesn’t even meet minimum consumption requirements, our rental fee or a tip to the staff for having to work an event no one even knows would happen free of cost.”