The Irish Competition Authority has ruled that Premier Foods' £1.2bn acquisition of RHM could “lead to a substantial lessening of competition in relation to gravy makers in the Irish market”.
Premier Foods would pick up RHM's gravy brand Bisto as part of the deal.
The Erin brand was acquired by Premier in August 2006 as part of its acquisition of the UK and Ireland businesses of Campbell Soup Company. For the year to 31 July, it recorded sales of £9m.
Last week, the Office of Fair Trading gave the merger the green light in the UK, revealing it would not refer the merger to the Competition Commission.
RHM and Premier Foods shareholders are expected to vote on the merger at separate meetings on Thursday (15 February).