Known as mooning, the cheeky offence was previously punishable under other laws but is now banned under specific legislation.
First-time offenders face up to two months in jail while repeat offenders could spend six months behind bars.
The amendment was one of more than 50 crimes included in an overhaul of sexual offence laws.
The updated legislation has been designed, in part, to separate pranks involving nudity from acts of sexual exposure.
