The European Commission said its preliminary findings suggest Ireland provided unlawful state aid to tech giant Apple for more than 20 years.
In a letter published today, European Commissioner Joaquin Almunia told Ireland it must provide details of the tax arrangements.
Almunia said any unlawful aid could be recoverable from Apple.
Five men have been arrested in connected with a drug-smuggling operation aimed at bringing cocaine worth up to £100 million into the UK.
Three British men were arrested on a yacht that was carrying the drugs on Tuesday morning. It had been tracked by authorities in several countries since setting sail from Venezuela.
The crew, which included a 70-year-old man, was reportedly sitting on bales of cocaine when the vessel was intercepted by an elite Navy squad 200 nautical miles the Irish coast.
A further two men were subsequently arrested by the National Crime Agency in the Leeds area.
Three British men are being questioned by Irish drugs squad officers after the yacht was intercepted with a suspected cargo of cocaine worth 80 million euro (£62.5 million).
The Irish Navy has only today released details of a huge drug haul which was discovered when they boarded a yacht yesterday.
The 60ft Makayabella was stormed 200 nautical miles off Mizen Head, Ireland's most southerly point before being towed to Haulbowline naval base in Cork.
The cargo of drugs, believed to weigh about a tonne, remains on the vessel at the dock while the three suspects are being questioned by the Garda.
If the haul of cocaine could have an estimated street value of 80 million euro, it could be even higher depending on purity. If confirmed, it would be one of the biggest such drug seizures at sea in Europe this year.
Three members of a family, including nine-year-old twin boys, have been found dead in a suspected double murder-suicide.
The youngsters were found dead in their home just outside the town of Charleville in north county Cork shortly before 5pm today.
About an hour later the body of a relative of the boys, believed to be aged in his early 20s, was found in a forested area about 10 miles away.
Garda detectives are not seeking anyone in connection with his death. Post-mortems are expected to be carried out tomorrow.
Gardai appealed for anyone with information to contact them at a police station or anonymously on 1800 666 111.
Pope Francis has paid tribute to the late former Irish prime minister Albert Reynolds for his work as a peacemaker.Read the full story ›
Former Irish prime minister Albert Reynolds has died at the age of 81, according to Irish media reports.
Reynolds served as Taoiseach (prime minister) for just under three years - one of the shortest ever terms - but is credited with making a significant contribution to pushing forward the peace process.
He is survived by his wife Kathleen, two sons and five daughters.
Cardinal Sean Brady, the leader of the Catholic Church in Ireland, has confirmed he has offered his resignation.
Amid much speculation that he was to stand down, the senior churchman said he wrote to Pope Francis last month asking if he could resign as Archbishop of Armagh.
"I did so in anticipation of my seventy-fifth birthday which I will celebrate tomorrow," he said in a statement today.
Archbishop Eamon Martin will take over the role as Archbishop of Armagh and Primate of All Ireland as soon as Pope Francis accepts the resignation.
An investigation is under way after a human leg was found at a recycling plant in Ireland.
The alarm was raised last night when the body part was discovered at the Thornton's plant in Ballyfermot in west Dublin.
Part of the recycling centre in Killeen Road has been closed down for forensic examinations to take place.
A tense stand off between US country star Garth Brooks and Dublin City Council over its cancellation of his comeback gigs in the Irish capital has ended without compromise.
On Tuesday Aiken Promotions announced with "great regret" that the US singer's five sold-out gigs planned for later this month at Croke Park were cancelled after the council granted permission for only three.
Brooks said that he would play "all or none" and today rejected a compromise to play three night-time gigs and two matinees, instead of the intended run of all evening performances.
The controversy even saw Irish Prime Minister Enda Kenny intervene, with RTE quoting him as saying that he hoped the offer of three evening shows and two matinees "would be a potential solution".
But the 'If Tomorrow Never Comes' star said that playing to 400,000 people over three days "cannot possibly compare" to five separate night concerts.
His publicist Nancy Seltzer said: "To treat 160,000 people differently than all the rest who will be seeing the show the way it was meant and created is wrong."
"He does not understand why it is once again put upon him to treat people less than they deserve to be treated and he still returns to why did they allow five shows to be sold and all these people to be disappointed.
"It is not his decision; it is, with the greatest of respect, the city council's."