The strike is an escalation of industrial action that began last Wednesday with a "work to rule" over stalled pay talks.
Public Service Association national secretary Richard Wagstaff said court and tribunal staff from had decided to strike because the ministry "continues to refuse to negotiate their pay".
"This is despite Justice paying its staff 6.3 percent below the median pay rate for the public service." Mr Wagstaff said the union had not put a figure on how much it was seeking in a pay rise for the staff it represented.
"We've simply identified how much Justice is underpaying its staff and have been trying to negotiate with the ministry on how we close that pay gap." Negotiations began four months ago when the two collective employment agreements for members expired, he said.
Union members had voted to continue the rolling strikes this week and next if the ministry "continues to refuse to engage in meaningful pay negotiations".
