The move follows a recent crackdown by gardaí in Dublin city centre, enforcing the Intoxicating Liquor Act 1988, which specifies that the latest opening hour for a Sunday nightclub is 1.30am on Monday morning.
Throughout the rest of the week, nightclubs can stay open until 3am. Both deadlines include a 30-minute drinking-up time.
"It was there in the act all the time and we saw it as a problem. The latest they could go was 1.30am, but they were going as far as they could, until 3am or more," said Inspector John Quirke of Pearse Street Station.
He said publicans inconvenienced by the late opening times had brought the matter to their attention. Gardaí at Pearse Street which covers the bulk of the city's nightclubs then started regular patrols of the clubs.
"We inspect any that are open and draw attention to the management that they don't have the licence to operate until that time," said Inspector Quirke. "We would then go back again. If they get caught enough their licence is in jeopardy and the fines start building up."
He said the operation had been ongoing for a number of months. "There are so many, it takes a while to get around. There are over 600 licenses."
Inspector Quirke said part of the problem was that there was no definition of a nightclub in the legislation.
Rather, there are a variety of licences, such as a publican licence and a theatre licence, of which there are roughly 15 in the city centre.
Other premises are hotels with public bars. There are around 25 premises that operate late on Sunday.
Among those hit by the garda operation are Spy, Rí Rá, Switch, Fitzsimons, The George, Capitol, Copper Face Jacks and Reynards.
Many of the clubs affected are angry at the sudden clampdown and have made representations to the gardaí.
"They're not happy with it, but until such time as the law changes we have to enforce it," said Inspector Quirke.
"We don't enforce 1.30am rigidly. If it is well after that we go in, and most of the places are well after that."
He pointed out that most clubs have complied with their directions, but added: "We will be going to courts in some instances, three or four, but that's down the line."