Autozone co-owner Jon Gardiner said officers ‘stormed’ the premises on Doncaster Road at around 6.45pm on Saturday, December 19.
They proceeded to take down details of the people there, warning they would issue each a £200 fine, he told the Chronicle.
The garage had closed at 6pm, as normal for a Saturday - but staff had stayed for an hour to swap presents and have a bite to eat, with two musicians asked to play festive tunes on acoustic guitars.
Jon, 41, said: “There were police officers storming through the front door with no reason.
“They could’ve walked in calmly.
“They could’ve done it with a phone call.
“But they’ve harassed me and my staff, and a couple of customers who were still in the shop - it’s not uncommon for us to stay anyway, if we have customers to help.
“We’ve had a lot of mental health and wellbeing issues within the staff, due to furloughing and letting people go.
“So we decided to have a bit of food, get a couple of guys playing Christmas songs on acoustic guitars - trying not to overstep the mark but put a bit of something together, for that wellbeing and moral support. Were we in the wrong?
“I was busy dealing with the police but my staff were shocked.
“I felt victimised.”
Jon said when he stood up to the officer, he was issued with ‘ridiculous’ requests that he knew he couldn’t fulfil - such as showing police his payroll to ensure all the people in the building were staff.
He added the firm employed 45 staff, around half of which were present on the evening.
“I think the police made their mind up before they came through the door what they were going to do,” he said.
“They saw what they wanted to see, which was a Christmas party.
“They’ve wasted a lot of resources, for nothing.
“The officer leading them read the riot act to me, and yet issued no paperwork. He should’ve listened to my explanation, apologised, and left, but was too emotionally-driven to walk away.”
Customer Lewis Tawton, from Wakefield, said he had been in the shop and then gone outside, before returning to find police who said they would be fining him for ‘attending an illegal gathering’.
“I was shocked,” said the 28-year-old. “Police were here, there and everywhere and I didn’t really have a clue what was going on.
“They took my name and address and said I would be fined, but I’ve not had anything come through.
“I felt a bit like a prisoner - I couldn’t leave until they said I could.”
Jon said the business has struggled to survive this year, with sales down by 70 per cent.
“For anyone in retail with big overheads like us, Covid has been catastrophic,” he added.
“We’ve had a hard year, like everyone. This has been the first time we’ve properly opened, we’ve put every precaution in place with stickers, directional signs, and signs on the front of the building - and then this happens.”
Jon said he would ‘wholeheartedly’ defend his staff if they faced any further allegations that they were breaking guidelines.
A police spokesperson said fixed penalty notices were issued to 30 people, with body-cam footage reviewed after the event.
“There was food, alcohol and a band playing,” they added. “This was clearly a pre-organised event and was a deliberate and blatant breach of Covid regulations.
“The company directors have also been reported for encouraging an offence.”