Ireland's corporation tax revenues are under threat as an international reform process kicks off in earnest.

The Organisation for Economic Co-operation and Development (OECD) is looking to change the way big technology companies are taxed.

It has now said it will consider moving to a system where companies will be taxed, at least in part, according to where users are based rather than where the company is based.

Ireland had opposed a similar plan at EU level, not least because a small population means it will reduce the tax take here - potentially hiking pressure to raise tax in other areas.

Corporation tax receipts have boomed here in recent years, putting the budget back into surplus. Losing those revenues would raise the prospect of having to borrow or raise other taxes to maintain spending.

"There's a limited number of users in Ireland and [the proposal under consideration] would obviously benefit the much larger countries," said Joe Tynan, head of tax and international tax partner at PwC Ireland.

"It kind of turns on its head everything that we've known before... if we were to tax Volkswagen based on where the cars were used I suspect you might find Germany wouldn't be in favour of it."

The OECD is a group of 36 countries of which Ireland is a member, alongside big economies like the US, Germany, Japan and the UK. Ireland has consistently said that the OECD is the correct venue for tax reforms, rather than the EU.

Though the process is not binding, for Ireland to refuse to implement a new system put in place would probably pose difficulties. If companies were being taxed one way in some of the bigger countries around the world, and another way in Ireland, that raises the prospect of 'double taxation', where companies are taxed twice for the same activities.

Given that the companies would want to continue selling their products to countries with big populations, Ireland could then see companies moving their tax residence out of here.

"The OECD's going to go through a process, and we have tended to stick with the OECD," Mr Tynan said. "If all those countries agree, because of our position as an international trading country we will have little choice but to sign it ... it's more than likely that we would feel obliged to sign up with that so that whether it's a US company or a German company operating in Ireland, that they know what the rules are and there's no double taxation."

Finance Minister Paschal Donohoe was in Davos last week trying to rally support for Ireland's consistently expressed view that companies should not be taxed according to where users are based. In high-profile public appearances both he and Taoiseach Leo Varadkar faced harsh criticism about Ireland's tax regime, highlighting the negative perception that some countries have about our system.

The OECD secretary general said the Apple case, whereby EU Commissioner Margrethe Vestager found Ireland had given a 'sweetheart' deal to the iPhone maker, was an example of 'gaming the system'. Both the Irish Government and Apple are appealing the ruling.

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