The National Lottery is urging people not to respond to calls offering free plays in the EuroMillions.
It is understood customers are receiving automated calls from a Dublin number telling them to press 1 if they want to take part.
However, Lotto HQ says it is nothing to do with the competition.
A National Lottery spokesperson said: "We have been contacted by several people in the last few weeks about such calls. We would like to reassure our players, and members of the public, that this activity has nothing to do with the National Lottery, and we would advise caution."
Spokesperson Miriam Donohoe said: "We are very keen to let the public know and our players know that this is nothing to do with National Lottery and we don't operate in this fashion at all."