The Competition Authority has blocked a takeover by Easons of books wholesaler Argosy.
In a statement the authority said: "Eason and Argosy are the only two Irish-based wholesalers of new books in Ireland, with Eason also being the leading retailer of new books."
It added that when it was informed of the transaction it began an investigation.
It said it "was concerned that the proposed transaction would have resulted in increased prices and a reduction in the range of new books to consumers".
In a statement today, Argosy Libraries expressed disappointment at the decision but said it was "business as usual at the company".