The Competition and Consumer Protection Commission (CCPC) says it is investigating potential bid rigging in the procurement of publicly funded transport services in parts of Munster and Leinster.
The CCPC opened an investigation last year after it received a complaint on the matter.
The commission has undertaken 20 searches in Tipperary, Waterford, Limerick and Kilkenny last July as part of the inquiry.
The CCPC says it opened an investigation in 2016, following an examination of a complaint.
As part of the investigation, the CCPC applied to local District Courts for search warrants to gather evidence.
It says authorised officers from the CCPC and Gardaí, including a member of the the Garda National Economic Crime Bureau, carried out the searches.
In a statement, the CCPC says: "This investigation is ongoing and the CCPC encourages any individual who has evidence to come forward and contact them.
"In addition the Cartel Immunity Programme operated by the CCPC, in conjunction with Director of Public Prosecutions, means that a member of a cartel may avoid prosecution if they are the first member to come forward, reveal their involvement in illegal cartel activity and fully co-operate with the investigation."