More than 1,700 Ministry of Justice staff who belong to the Public Service Association went on strike for an hour on Tuesday morning.
The PSA says that the staff are paid 6% below the public-service median rate but that the ministry is refusing to engage in talks.
Two weeks ago Justice staff undertook a first round of industrial action by refusing to do overtime.
PSA national secretary Richard Wagstaff says that unless proper talks begin, a campaign of rolling strikes will continue till the end of next week.
He says some Justice workers, who typically collect fines and work at courts or tribunals, are being underpaid by up to 13%.
