Sinn Fein has claimed that the annual £9bn subvention from the British Exchequer to Northern Ireland is a myth and that Irish unity is economically viable.
Writing in today's Belfast Telegraph, TD Pearse Doherty said his party has engaged with the Office of National Statistics (ONS) to break down Northern Ireland finances.
Acknowledging that genuine concerns exist about the subvention - a grant of money - he argues that there would instead be a £4bn shortfall in the event of a united Ireland.
Mr Doherty said: "For 2017-18, the ONS state that £26.463bn was spent in the north of Ireland, while £17.3bn was raised in taxes. The difference between these two figures (about £9bn) is what people believe to be the subvention - this simply isn't the case.
"Importantly, £3.4bn of this figure is paid out in pensions each year. This would remain the responsibility of the British government in the event of Irish unity, and is already the case for many people living in the south of Ireland who receive a British pension, having paid national insurance contributions during their working life."
The Donegal TD said that a further £1.27bn went towards Britain's £1.8tn national debt.
"This cost would be subject to post-unity negotiations, and when it is, a firm principle must be followed - if the North is made to retain liability for British debt, then it must gain the exact same proportion of British-owned assets," he said.
"£1.1bn of spending on the British military wouldn't exist, and almost all of the £679m 'Outside the UK' spending would vanish.
"When £3.4bn of pension payments are removed, and additional corporation tax is factored in, the mythical subvention figure of £9bn could be slashed by at least £5bn. The remaining £4bn could easily be subsumed into the public finances of the Irish state over time."
Mr Doherty noted that the Republic had one of the fastest growing economies in the world in recent years.
"Two economic reports by Dr Kurt Hubner model an Irish unity dividend, one of which points to an additional €23.5bn for the island economy in a post-Brexit scenario," he said.
"The economic case for Irish unity is evidence-based and clear-cut. The £9bn subvention figure is a myth designed to paralyse debate on Irish unity, and few people who use the figure actually understand it.
"Irish unity will reduce costs in the north and unleash the potential of the all-island economy within the European Union."