Up to 1,000 households stealing gas in Belfast were today offered an amnesty from prosecution.
But supplier Phoenix Natural Gas warned it will go after anyone who keeps tampering with meters.
Some involved in the scam are believed to be charging up to £60 (€89) a time to rig up the electronic household equipment. Engineers are set to examine meters in a bid to uncover how much has been used without payment.
Although Phoenix has vowed that all involved in the racket will be detected, general manager David Strahan urged them to come clean.
"We can give a commitment that those who come forward voluntarily we will not seek to prosecute," he told BBC Radio Ulster. "However, if people persist in this activity and continue, it's only a matter of time before they are identified to us.
"We can identify from our office, from our billing system, from looking at payment histories, we can identify the people engaged in this activity.
"We will catch up with them, and we will seek to recover the money from them and we will seek to prosecute them."
PA