The European Commission will rule against Ireland and its tax arrangements with the US multinational Apple tomorrow morning, RTÉ News understands.

In a document running to 130 pages, the commission will rule that Ireland's tax arrangements with Apple amount to illegal State aid.

The amount of money the company will be asked to pay the Irish tax authorities will be contained in a ballpark figure which will be announced by the EU's competition commissioner, Margrethe Vestager, tomorrow morning, RTÉ News understands.

The decision has been eagerly awaited on both sides of the Atlantic.

Last week the US Treasury Department issued a stinging attack on the commission's investigations into the tax affairs of Apple, as well as the probes into Starbucks, Amazon and Fiat.

The announcement will conclude a bitterly contested three-year investigation by the European Commission into two alleged sweetheart deals struck between the Revenue Commissioners and Apple in 1991 and 2007 respectively.

RTÉ News understands that Commissioner Vestager circulated her findings among the other 27 commissioners at 10.00am Brussels time.

The College of Commissioners has until 10am tomorrow to raise any objections.

This is thought highly unlikely. After that Commissioner Vestager is expected to make the formal announcement during a news conference.

The Irish Revenue Commissioners will then be mandated to use the commission’s methodology in calculating how much tax the commission believes that Apple owes the Irish State.

In a similar ruling against the Netherlands, the commission required the coffee chain Starbucks to pay between €20m and €30m in back taxes.

That case has been appealed to the General Court of the European Court of Justice.

One estimate by JP Morgan put the Apple figure at $19 billion, but it is thought the figures will be considerably smaller than that.

In its preliminary ruling, issued in 2014, the commission argued that Apple had received letters of comfort with the Revenue Commissioners in 1991 and 2007 which gave the company an unfair tax advantage over other companies.

The Irish Government, and Apple, have consistently denied any breach of State aid rules.

The Government has said it will appeal any negative decision to the ECJ.

Fianna Fáil Finance Spokesperson Michael McGrath earlier said his party will not take a final position on the ruling until its members read the EU Commission's report and see the response from the Irish authorities.

However, speaking on RTÉ's Today with Sean O'Rourke, he said his party has accepted in good faith the reassurances it has been given on the matter, that it had no evidence to the contrary, and if that remains the case it will certainly support an appeal by the Irish authorities to the European courts on those grounds.

Mr McGrath said Apple is a very important part of the economy in Cork and will soon employ close to 6,000 people there, so this is not "a brass-plate operation where monies are coming into Ireland through some intricate funding system.

“This is a real operation, but the question is have they been treated fairly and consistently with other companies in relation to Ireland's corporation tax.

“We have been reassured so far that they have, so that remains our position and we will read the report very carefully and the Irish Government response," he added.

However, Sinn Féin’s Finance Spokesperson Pearse Doherty said the Government should rule out an appeal if the EU Commission rules that Ireland provided illegal state aid to Apple.

Mr Doherty said: "Tax, and the State aid rules, is not just for the man in the street or the local business. They must apply to everybody. The days of nod and wink arrangements must end. There is no logical reason to appeal a ruling against the State.”

The Anti-Austerity Alliance has also called on the Government not to appeal against any adverse finding.

AAA TD Paul Murphy said: "The EU Commission seems to be on the verge of exposing one of the sweetheart deals which multinationals benefit from in Ireland and in the process could gain potentially billions in unpaid taxes for the State.

“Working class people will see straight through the Government spin that it isn't that much money or that it couldn't be used for public services or housing.

“The essential facts of the matter is that while we have massive crises in our public services and an unprecedented housing crisis, the Government is prepared to fight tooth and nail to prevent Apple paying money it owes which could be used to resolve those crises,” he said.