The £240 million float of online holiday company On the Beach is reported to be at the heart of a probe into alleged rigging of share prices by fund managers.
The 2015 listing is among three deals being investigated by the Financial Conduct Authority (FCA), sources told The Sunday Times.
On the Beach said it knew “absolutely nothing about this matter” until contacted by the newspaper.
The regulator last week reportedly accused Newton Investment Management, Hargreave Hale, Artemis and River and Mercantile of colluding on two floats and one share placing in 2014 and 2015.
Newton is understood to have dismissed one of its most senior fund managers over the affair.
The firms are alleged to have worked together to pick up stock on the cheap. If the FCA proves its case, they could be fined up to 10% of their worldwide revenue.
They could also face damages claims, although victims could struggle to quantify their losses. Shares in On the Beach fell in the months after listing, but have more than doubled in price since.
River and Mercantile, Hargreave Hale and Newton bought sizeable stakes in On the Beach at the listing, according to the Sunday Times.
More: On The Beach sees profit growth despite £2 million Monarch hit
On The Beach would consider acquisitions for long-haul and overseas growth