Prostitution activity in the North has been driven south of the border in order to beat a new law which makes it an offence to buy sex.
The Immigrant Council of Ireland has said online prostitution in border counties in the Republic has jumped by more than 50pc as pimps move their operations to escape the law, which came into force yesterday.
Northern Ireland is the first country in the UK to pass the law, which means sex buyers could be hit with a year in prison and be faced with a £1,000 (€1,390) fine.
Members of the North's Assembly voted by 81 to 10 in favour of the measure, brought by the DUP peer Lord Morrow.
In the Republic it is not an offence to buy sex.
The Immigrant Council has produced figures showing that the number of online profiles on escort agency websites in Donegal, Cavan, Monaghan, Leitrim and Louth has increased from 51 to 77 in advance of the law coming into force.
In Louth, there were 25 escorts advertising their services at the end of May compared to 18 at the beginning of the month. Numbers were up from 14 to 24 in Donegal, from two to nine in Leitrim and from 13 to 15 in Co Cavan.
"Brothels are inclined to move quite often, and the vast majority of prostitution is now organised online through chat rooms and websites, and our figures show the changes since the start of May," said Brian Killoran, Chief Executive of the Immigrant Council.
While he welcomed the new law in the North, he urged authorities and the government here in the Republic to follow-through and introduce similar laws here.
"An all-Ireland approach is needed in order to provide the maximum effect and protection for people who have been and are being trafficked," Mr Killoran said.
"In the North it only took 18 months to bring the matter from debate to law, but here the debate has taken six years and it was two years ago an Oireachtas Joint Committee backed the law with cross-party support," he added.
"It is important that Gardai monitor the increase in online activity and use our existing laws to ensure that pimps and traffickers are not viewing our border counties as safe havens after their business model has been wrecked in the North," Mr Killoran said.
"It is also essential that the Justice Minister Frances Fitzgerald honour her commitment to publish sex buyer laws here and that we join Northern Ireland, the US, Canada and Sweden in shutting down the organised crime behind prostitution," he added.
Denise Charlton, anti-trafficking consultant with the Immigrant Council, said: "There is no denying that during the month of May a trend has emerged in online prostitution, with more and more profiles being established in our border counties.
"Now the law is a reality we expect to see this increase even more."