The Ministry of Business, Innovation and Employment has issued 23 warnings to retailers they believe may be tempted to ignore Easter trading laws again.
It is illegal for shops to trade on Good Friday and Easter Sunday unless they have an exemption under the Shop Trading Hours Act.
The ministry refused to say how many businesses opened on Friday in defiance of the law, saying it intends to announce a total number at the end of the long weekend.
Businesses that flout the law can be fined up to $1000.
The ministry says the 23 warnings were given to businesses that opened in 2012 and which may be tempted to do so again this year.
It is understood the ministry achieved 30 convictions for illegal Easter trading last year.
Retailers Association spokesperson Barry Hellberg says shopkeepers should have the choice to open if they want to on Good Friday and Easter Sunday and the current law isn't working.
"Unfortunately, the Government won't institute any inquiry and in the last few years there have been a number of private members bills which regrettably have not got through the process.
"So until the Government actually decides to take the high ground and look at a problem which a lot of people seem to flout then, quite clearly, the law's an ass and it needs to be reviewed."