A Christchurch bar owner says he probably shouldn't have called a group of customers "tossers" on Facebook after only half their booking showed up - and refused to pay for the extra food prepared.

But Mark McGuinness said people needed to realise flaking on big bookings cost businesses dearly - in wasted food costs and lost revenue from turning down other bookings.

McGuinness, who owns the Belgian Beer Cafe Tarenhof in central Christchurch, admitted he "boiled over" a little when posting about a group booking for 40 people from the Canterbury District Health Board on Saturday night.

"Platters are made for their 6.30 arrival. The lass who booked it turns up at 6.45 and guess what, there's only 20 of them," his post on the venue's Facebook page read.

"Do they want to pay for the non-attenders, they refused to pay a deposit, treat us like ... well you guess, expect exceptional service and we lose money. Oh well that's hospo."

The post ended by saying the cafe wouldn't be accepting any more bookings from the CDHB, calling them "tossers".

McGuinness confirmed he had written the post, which had since been deleted after comments below it started to get out of hand.

Many commenters said they thought the post was unprofessional and said it made them hesitant to visit the venue.

"Wow a business slagging off their customer," one comment read.

"Not very professional and a bit off-putting."

Others said it was good to see the venue staff standing up for themselves.

McGuinness apologised for using the word "tossers", but stood by his right to be angry with the group.

A set menu for 40 people had been ordered on Friday when a staff member rang up to confirm the booking, but when the group arrived on Saturday only half were present.

When the bar's manager told the group they would need to pay for all the platters the venue had prepared, they were laughed at, McGuinness claimed.

"Whenever you're making a booking in a restaurant ... we survive on bums on seats," he said.

All in all McGuinness guessed the no-shows cost him up to $2000 in lost turnover because extra staff had been put on, food ended up wasted and he had turned down other bookings to accommodate them.

"They tie up resources making a booking of that size and we have to wear it."

A CDHB spokeswoman said they employ over 10,000 people.

"We are not aware of, or responsible for, what staff do outside work hours. We are not aware of any 'CDHB Event' as referred to below and we have not seen the Facebook post.​"

McGuinness said unreliable bookings were an industry-wide problem and Christchurch's hospitality industry had had a lean winter.