The financial regulator is to investigate unusual trading patterns in Irish shares.
The development follows a similar investigation by the UK's financial regulator into shares in Halifax Bank of Scotland.
Shares in Ireland fell by 4.6% on St Patrick's Day, but the sharp drops in shares many not have been simply caused by concerns about the slow down.
The financial regulator says it is concerned that false and misleading rumours circulating in markets are the cause.
Its prudential director Con Horan said market participants who take unfair advantage by spreading false rumour while trading on those rumours are in breach of abuse regulations.
The regulator will actively pursue those who may be engaged in this, he adds.
Some hedge funds have spread rumours about Irish banks sold the shares at a high price bought them at a low price and made money on the difference.
On St Patrick's Day, Irish banks were down 7% and shares in Anglo Irish Bank were down 23% at one point.
One senior banker told RTÉ News that there has been skullduggery and the greater the volatility the greater the skullduggery among market participants.
