The European Commission, which has been investigating the Apple deal for more than two years, said on Wednesday that Irish authorities had not responded fully to an earlier query.
(Also see: EU Says Apple's Irish Tax Deals Breach Rules)
"Ireland did not reply in full to the Commission's last request for information, which is why the Commission has sent a reminder to Ireland to request the missing data," Commission spokesman Ricardo Cardoso said in a statement.
"Furthermore, the Commission has requested clarifications to follow up on some of the replies sent by Ireland," he said.
The Irish finance department said it has provided a detailed response, saying an EU ruling was not imminent.
"There is simply no question that the Irish authorities sought to give the company in question any kind of special tax deal," a finance department spokesman said.
The EU competition enforcer in 2014 accused Ireland of swerving international tax rules by letting Apple shelter profits worth tens of billions of dollars from revenue collectors in return for maintaining jobs.
(Also see: Apple May Be on Hook for $8 Billion in Taxes in Europe Probe)
Apple's vice-president of its European operations, Cathy Kearney, told a European Parliament hearing on Tuesday that the company had paid every cent of its taxes in Ireland.
Starbucks, Fiat Chrysler Automobiles, AB InBev, BP and BASF are among companies facing millions of euros in back taxes after the European Commission ruled against their tax deals.
© Thomson Reuters 2016
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