Five-a-side football firm Goals Soccer Centres has uncovered "substantial" VAT errors totalling £12m so far, but has warned the final cost is not yet known.
It said the mistake went back "several years" and it needed more details to establish the full cost of the blunder.
The new VAT accounting policies it will now need to adopt "may have an impact on future profitability", Goals warned.
Shares have been suspended because the error could lead to "a material change" in its financial position, it said.
The firm, which operates 50 outdoor football centres in the UK and California, says it plans to enter into discussions with HMRC immediately.
"The value associated with these errors is still to be finalised but remains significant," it said.
The group added it would make "further announcements in due course as the results of the investigation become known".