British Prime Minister David Cameron's opt-out of the latest European political deal could give London's financial sector an international advantage, Fianna Fail has said.

Finance spokesperson Michael McGrath expressed fears the British government move could have serious consequences for the future of the financial services industry in Ireland.

He said the Prime Minister rejected the European Union (EU) proposals to protect the City of London.

"Given that a new financial transactions tax is likely to form part of the new arrangements that will apply to the other 26 EU countries, this could put Ireland's financial services industry at a major disadvantage compared to London," he said.

"We could soon have a situation where the financial services industry in Ireland will be subject to a new transactions tax, but the City of London will be exempt. Such a scenario could have serious ramifications for what is a critically important industry in Ireland.

"The financial services industry is highly mobile and we cannot allow a situation where London becomes a more attractive base than Ireland because of a new tax."

He said the sector employed more than 30,000 people in the Irish Republic and was a major contributor to its economy.

"The Taoiseach Enda Kenny needs to urgently clarify if Ireland has committed to a new financial transactions tax and to state clearly what the implications of such a tax would be for Ireland given that the UK will be exempt."

Michael McNamara, a representative of coalition government partners Labour, said the Fianna Fail comments were opportunistic.

"The latest Fianna Fail fad is to follow David Cameron's eurosceptic agenda," he said. "Of course, we realise that a transaction tax, like other fiscal harmonisation measures has to be carefully considered. However, there can be no blanket exemptions, least of all for those who contributed most to the mess we're in."