Road Policing Senior Sergeant Ian Row confirmed that from August 11 to September 30 Northland officers had issued seven fines and given five others written warnings.
He said officers had warned the window washers initially. "It had a massive effect straight away and we are just going to enforce it now."
The new legislation, clause 11.6A, washing of vehicles, says a pedestrian must not wash or offer to wash a vehicle, or part of a vehicle on a road unless it is legally parked.
The Whangarei District Council made a submission supporting the changes.
WDC staff considered a nationalapproach was appropriate and the power to issue fines would provide a much-needed simple and low-cost tool.
Four major intersections previously frequented by the window washers around Whangarei came under the control of the New Zealand Transport Agency and outside the jurisdiction of the council bylaws.
Whangarei Mayor Sheryl Mai welcomed news that police were able to issue $150 fines.
"Our council lobbied central government to make this alteration to the act. We are pleased that police can now issue instant fines, although we do realise the change puts a new workload on to them, Ms Mai said.
"We all hope the fines prove to be a fast deterrent to the window washers."
Sarah Azem of New Zealand Transport Agency said as the agency was not enforcing the fines they would not comment on the law change and what impact it might have.