Police are hoping to boost convictions of motorists who warn others of speed cameras by taking a lorry driver's case to the House of Lords.
The Crown Prosecution Service (CPS) wants to overturn a court ruling in which Charles Glendinning, of Somerset, was cleared of obstructing police duty.
The High Court found police could not prove drivers had slowed down as a result of his waving to them.
A CPS spokeswoman said there was an issue of law that needed clarification.
Mr Glendinning, a milk tanker driver, had first been convicted of obstruction by Yeovil magistrates.
In October, High Court judges decided there was no proof his gestures had been seen by speeding drivers, and was therefore not "obstructive".
The CPS appealed against the ruling, but the case was dismissed by the Court of Appeal.
The CPS has now referred the case to the Court of Appeal's administrative court seeking leave to appeal to the House of Lords.
The request said: "For there to be an obstruction of a Pc in the execution of his duty by getting in the way of a police speed trap, is it necessary for the prosecution to prove that those warned were exceeding the speed or were likely to do so at the location?"
Paul Smith, founder of the Safe Speed road Safety campaign, said: "Motorists warning others of speed traps is extremely effective in slowing traffic. If they don't want our money, then why appeal this case?"