Speed camera operators are planning to strike over the October bank holiday weekend.
Workers at national speed camera contractor GoSafe will ramp up industrial action in a row over union recognition and working conditions.
Their union Siptu served notice on the company this week of a three-day strike beginning on Saturday, October 26, and ending the following Tuesday.
In addition, the workers plan a work-to-rule from next Wednesday, when they will refuse to co-operate with an IT tracking system.
"We're extremely disappointed that neither the company, the minister or gardai seem to have any interest in resolving a very serious dispute that could have serious implications for road safety in the country," said Siptu organiser Brendan Carr.
The union sought a pay rise and claimed members did not have adequate breaks or toilet facilities.
It accused GoSafe of ignoring a Labour Court recommendation to recognise the union.
"If gardai step in, it will take them from crime-fighting duties," said Mr Carr.
Justice Minister Charlie Flanagan urged all those concerned to seek a positive resolution to the dispute "through the appropriate channels".
"The minister is unable to intervene in a dispute between the contracted service provider and its employees and members of Siptu," said a department statement.
A garda spokesperson said: "An Garda Siochana does not comment on industrial relations matters between a contractor and its employees," adding the force would continue to monitor the situation.
Ahead of the previous strike, a garda spokesperson said the garda National Roads Policing Bureau met with GoSafe managers to put in place a contingency plan.
It said this was designed to ensure the effective monitoring of speed limits.
GoSafe would provide up to 50pc capacity and garda road policing units would make up the shortfall "with high visibility speeding intercept operations".
A GoSafe spokesperson was not available for comment.