An NOI is a formal document filed in court by a company or its directors, to inform parties the company intends to enter administration, a process aimed at rescuing a struggling business from liquidation.
Lynn Glaister, chairwoman of the CF10 Rugby Trust – an independent voice for supporters – said they were "shocked" and "gutted".
Speaking to BBC Radio Wales Breakfast, Ms Glaister said "something has gone wrong" with the investment in the club agreed as part of last year's takeover by investment group Helford Capital Limited.
She added "questions have to be asked about that", reassuring members her organisation would do all it could "to ensure the survival of our great capital city club".
"We now need to look to the future," she said.
"Cardiff Rugby has been around since 1876 and we need to ensure we are around for our 150 year anniversary and for many decades beyond."
