The Environmental Protection Agency (EPA) has confirmed that it is aware that thousands of tonnes of commercial waste from the Greater Dublin area are being dumped across the Border every week.
A spokeswoman for the EPA said the practice was widespread, but blamed the landfill sites in the North for the problem.
"The EPA is aware that this is happening, and we are monitoring the situation. However, the responsibility is mainly on the destination - it is up to them to refuse acceptance of the waste."
The Irish Times has established that in recent months hauliers in Northern Ireland have started to lobby waste contractors in the Republic for waste haulage business on a regular basis.
Nearly all these Northern hauliers are operating illegally because they do not have the necessary licences.
A spokesman for the Garda Press Office said gardaí were investigating "a number of cases" of illegal waste dumping.
Under EU rules, non-hazardous waste can only be exported for recycling or recovery. However, The Irish Times has learned that the bulk of this commercial waste is being illegally dumped in landfill sites in Northern Ireland.
Up to eight waste contractors in the Greater Dublin area are engaged in this practice. Under the terms of their licences, all waste contractors must record the final destination of their waste.
The cost of disposal at landfills in the North is much lower than in the Republic, and the savings are enough to justify the cost of the long haul.
Landfill charges in the Dublin area average about €150 per tonne, while charges in the North average about €90 per tonne.
It is understood that a small number of the waste shipments being exported are recycled - in accordance with the law - but the vast majority are being dumped illegally in landfill sites across the Border.
The vast bulk of this waste is being transported by Northern Ireland-based hauliers, who do not have the required waste collection permits and trans-frontier shipment documentation.
Industry sources say the responsibility for policing this lies with local authorities on both sides of the Border.
They claim the illegal practice is a result of the failure of local authorities to develop adequate waste disposal capacity in the Greater Dublin area.
The chairman of the Irish Waste Management Association, Mr Jim Kells, told The Irish Times he had heard "rumours" of illegal dumping of commercial waste across the Border.
"If commercial waste is being exported in accordance with the law, we have no problem with the practice. However, if this is being carried out without the necessary papers and documentation, we would condemn it unreservedly," said Mr Kells.
A report by Peter Bacon and Associates, published in July 2002, estimated a deficit in landfill capacity of 400,000 to 500,000 tonnes per annum in the Greater Dublin area for the period 2002 to 2009.