Gold Cup favourite Kemboy could be barred from running for the foreseeable future following a ban on entries and declarations registered in the ownership of Supreme Horse Racing Club.
The syndicate's horses are all trained by Willie Mullins and its star name won the Punchestown Gold Cup in May.
Horse Racing Ireland has requested answers from Supreme on what it says are "a number of queries and concerns".
The syndicate declined to comment when contacted by the PA news agency.
In a statement, Horse Racing Ireland's owner relations manager Aidan McGarry said: "Horse Racing Ireland has engaged with Supreme Horse Racing Club to seek information to resolve a number of queries and concerns.
"Following an unsatisfactory response from Supreme Horse Racing Club, Horse Racing Ireland, under Horse Racing Ireland Directive 15, has suspended Supreme Horse Racing Club's ownership accounts from all activity, including the running of horses from Monday, 21 October.
"At all times Supreme Horse Racing Club was aware that the penalty for the non-delivery of the information requested by Horse Racing Ireland would be that a hold would be put on all entries and declarations for horses registered by Supreme Horse Racing Club."
Kemboy had been in line to make his seasonal reappearance in the Ladbrokes Champion Chase at Down Royal on the first weekend of November.
Other notable horses owned by the syndicate include Aramon and Cadmium, a winner at last season's Grand National meeting.