Lawyers for the Oyston family have told a High Court registrar of "concerns" that money-laundering cash may have been used to help fund Blackpool FC.
The club's owners raised the issue at a preliminary hearing in a legal battle with Latvian Valeri Belokon, the club's president and 20% shareholder.
They said that a bank owned by Mr Belokon was fined one million euros for repeated money-laundering "violations".
Mr Belokon who is alleging "unfair prejudice" denied the claim.
Eric Shannon, representing owner Owen Oyston and chairman Karl, his son, added the fine, on Mr Belokon's Baltic International Bank, was for "transactions that subjected the bank to a significant money laundering risk".
Fraser Campbell, representing Mr Belokon, told registrar Sally Barber at the hearing in London that the allegations were "wild and extremely serious" and which they had "responded to in a detailed letter setting out precisely the source of the funds involved."
Mr Belokon has accused the Oystons of stripping the football club of funds and is pursuing a claim for "unfair prejudice".
The hearing heard that Belokon's company, VB Football Assets, bought a 20% share of Blackpool FC for £1.8m in July 2006 and advanced £2.7m of loans "on highly generous terms" to the Oystons and their company Segesta Limited.
They also made money available to buy players and consequently the club was promoted to the Championship and, in 2010, to the Premier League.
VB Football hoped to convert the loans into a further 30% of shares, documents before the court revealed.
The documents also stated: "Promotion to the Premier League produced unprecedented revenues for the company, particularly in respect of television rights.
"However, instead of investing those funds in, for example, a strengthened playing squad, or using them to pay dividends to shareholders, the respondents (Segesta and the Oystons) caused enormous sums to be transferred to themselves and their associated companies."
Segesta and the Oystons deny unfair prejudice and are fighting the claims.
Blackpool supporters are set to march through the town ahead of Saturday's lunchtime fixture with Wigan in protest at the club's plight.