NSW Labor leader Michael Daley has given an "ironclad" guarantee that he would not water down gun laws as the Liberals step up pressure and roll out anti-gun advertisements featuring John Howard.

The Liberals delayed the release of the ad for two days following the Christchurch terrorist attack, but published it on social media on Sunday night.

In the advertisement, Mr Howard says the Shooters, Fishers and Farmers had wanted his signature 1996 gun laws repealed and would put "enormous pressure" on Labor to do so if they were to win.

The Coalition has been campaigning strongly on Labor's decision to swap preferences with the Shooters in Barwon and Murray, seats the Nationals fear they could lose in Saturday's election.