Maurice Regan, the US-based building tycoon, has filed a High Court action against billionaire racing boss John Magnier and his stud business, alleging they have breached competition law by barring Regan from using an equine hospital and Coolmore Stud.The legal action escalates the conflict between the two billionaires that began when they clashed in 2023 over rival bids for the Barne Estate farm outside Clonmel.In a legal action filed on Friday, Regan’s Newtown Anner Stud Farm Ltd, which is also based outside Clonmel, has sued Magnier, his son MV Magnier, Linley Investments trading as Coolmore/Castlehyde and Associated Stud Farms, Trans European Transport Ltd, and Coolmore executives Michael Ryan, William Macksey, Jerome Case, Paul Shanahan and David Wachman. O’Byrne & Halley Veterinary Surgeons Ltd, Fethard Surgical Ltd and Equine Diagnostic Laboratory Ltd, in which Magnier has ownership interests, are also named as co-defendants. The High Court summons alleges the defendants have breached Irish and EU competition law through anti-competitive practices and abuse of a dominant position in the market.Newtown Anner Stud is seeking a declaration prohibiting Magnier and Coolmore from instructing, directing, inducing, threatening or otherwise causing any third party including the Fethard Equine Hospital from ceasing or disrupting services to it.Mares and foals graze beneath Slievenamon at Coolmore Stud in Fethard, Co Tipperary. File photograph: Dara Mac Dónaill The Regan stud wants a declaration that any concerted practice between the defendants that led to the Fethard Equine Hospital ceasing its provision of veterinary services to Newtown Anner is a breach of EU competition law. Newtown Anner Stud is also seeking an order that the defendants provide goods and services, including the provision of “covering services” and veterinary hospital services, on terms no less favourable to those made available to other businesses.The legal case from Regan’s stud farm also seeks an award of damages, which includes damages “for causing loss by unlawful means and/or intentional interference with economic relations”.Regan was described as a “dark force” by lawyers for Magnier last year in the Coolmore owner’s unsuccessful action against the Barne Estate that sought to stop the Thomson-Moore family from selling their 751-acre home and farm to Regan for €22.25 million.The High Court heard that in 2023 Regan wrote in a text to a third party that he hooped a newspaper article about his bids for Barne would give Magnier a “heart attack”.Maurice Regan alleges John Magnier and his stud business breached EU competition law. Photograph: Collins Courts Last January a Coolmore source said the “heart attack” comment and others from Regan were among the reasons Regan’s horses were no longer welcome in Coolmore or the Fethard Equine Hospital.“Where a Coolmore client has made threats and expressed a hope that its principal will have a heart attack, that’s hardly conducive to good client relations,” the source said. “It’s not the sort of business Coolmore either wants or needs, and I imagine that also applies to its various investments including Fethard Equine Hospital.”The Coolmore source said the decision to cut professional links with Regan was a cautionary measure, citing issues of security, as well as reputational and safety concerns for Coolmore.[ Man to face trial over three counts of attempted murder following Stoneybatter attacksOpens in new window ]In response to the move to block Newtown Anner’s access to Coolmore and the equine hospital, a spokesman for Regan said in January they were “extremely surprised” by the “lack of sportsmanship and this unjustified attack on the welfare of our horses”.“How can it be normal or proper that Coolmore can control which veterinary practice can receive and care for Maurice’s horses at Newtown Anner Stud? What is going on? Bulldozer law continues,” the Regan spokesman said.Asked about the “heart attack” comment in the stand in the Barne case, Regan said it was Magnier who told others that he was “at war” with him.“So, all’s fair in love and war,” he said.Magnier had denied being “at war” with Regan, but told they court they were “at loggerheads about buying land”.“In fact, to this day we’re doing business every day,” he said in the stand last summer.Regan made his fortune through his New York-based building firm JT Magen. He also owns the Mercantile Group, which has 11 pubs and venues in Ireland that include well-known Dublin bars Café en Seine, The George and Whelan’s.His spokesman declined to comment on Friday. A Coolmore spokesman said it declined to comment on matters that are the subject of legal proceedings.