Gardaí in Co Donegal are on high-alert following plans by hundreds of rally fans to converge on the county this weekend.
The weekend should have marked the traditional Donegal International Rally event, which has been cancelled due to Covid-19.
However, gardaí say they are aware of plans of car enthusiasts to come to Letterkenny to mark the occasion.
Details of a number of illegal 'diffing' events have already been posted on social media.
Garda Sergeant Eunan Walsh warned car enthusiasts that gardaí will be out in force this weekend and will not tolerate any illegal behaviour.
As well as random checkpoints, there will be an increase in speed checks.
He said gardaí are aware of a number of 'diffing' events in controlled environments but there are fears of diffing at other uncontrolled events.
"This is normally the biggest weekend of the year for rally fans when they converge on Letterkenny and Donegal but that is sadly not happening this year," he said.
We will be operating a zero-tolerance approach to any bad driving
"We are aware that accommodation has been booked out and that these people will be arriving in town to mark the occasion.
"We want the message to go out that we will be operating a zero-tolerance approach to any bad driving.
"We will be out in force and will be operating high visibility patrols, speed checks and checkpoints across the weekend.
"We are asking people not to gather in groups and not to engage in any illegal activity," he said.