Copyright notices have begun flowing in to internet providers, with Telecom confirming it received 42 infringement notices overnight.
The notices were all sent out by the Recording Industry Association of New Zealand (RIANZ).
Of the 42 notices received by Telecom, 35 were for the download of songs by Rihanna, six were for Lady Gaga tunes and one was for UK recording artist Taio Cruz.
TelstraClear has also confirmed that it received 27 notices overnight from RIANZ, although the company would not say what copyrighted material the notices covered.
Internet provider Orcon received its first copyright notices overnight, two months after controversial anti-piracy laws came into effect.
Five of the six infringement notices were for the download of songs by R&B star Rihanna, Orcon chief executive Scott Bartlett said.
The "three strikes" law requires internet companies to issue warning notices to customers suspected of illegally downloading copyright content - such as movies or music - if a rights holder requests it. After a third notice, rights holders can bring a case before the Copyright Tribunal, which can fine an offender up to $15,000.
It was passed under urgency in Parliament in April and came into effect on September 1.