The Government may face a collective lawsuit involving costs of up to $2 billion from 4,000 Correctional Services officers claiming they have been underpaid for overtime work.
The Correctional Services Officers' Association will spend the next 30 days gathering opinions from members for the legal battle.
The move followed the victory last month of Chief Officer Shau Lin-chi, 49, who claimed compensation for 1,645 hours' overtime at High Island Vietnamese detention centre.
The court ruled the father of five was entitled to nearly seven months' paid leave as he was paid only $3.28 an hour for the overtime.
The association estimated about 4,000 of the 6,600 correctional services officers had performed the 'overnight on-call' duty.
Unlike other disciplined services which only require staff to carry a pager, Correctional Services Department staff have to be present.