Motherwell have demanded Cardiff settle a 'substantial' overdue instalment of the transfer fee due for defender Paul Quinn.
Quinn joined Cardiff last summer for a fee reportedly in the region of £300,000 but an instalment due in January has still not been received, according to the Scottish club.
The Bluebirds finally paid off a tax bill to Her Majesty's Revenue and Customs last month to stave off a winding-up order, but their debt to former owner Sam Hammam and the Langston Corporation is believed to be around £15million.
Well chief executive Leeann Dempster has revealed the Fir Park outfit have run out of patience with Cardiff and are demanding the money they are owed.
"The board have been very patient with Cardiff given the financial pressures they have faced," Dempster told the club's official website.
"However, the interests of our shareholders, employees and fans are being jeopardised by the failure of Cardiff City to pay the debt that they have outstanding.
"We have made clear to the board of Cardiff that we are left with no option but to pursue every possible avenue of recourse to secure our own club's interests. We hope that this matter can be resolved in an orderly manner."