Labour's Lewis MacDonald has welcomed the proposal to reduce the limit but said it could potentially have resource implications at a time of cuts to police backroom staff.
"I am not, in principle, opposed to the further devolution of more powers in this area but I am concerned to see the legislation come forward using the powers that are devolved already in order for that to provide the basis to go forwards," he said.
Mr MacDonald praised the former Labour government at Westminster for commissioning Sir Peter North's independent review of the law on drink and drug driving.
"Random testing, for example, was one of the North recommendations that he was able to elucidate strong evidence for," he said.
"I think some of the other issues raised are less evidence-based but I don't think the priority at this stage is the debate around those powers.
"The priority is to ensure that the powers that we have are implemented effectively."
More top news
Hundreds of hotels in the UK have poor food hygiene ratings, some which need improvement urgently, but are withholding them from the public.
Delivery company Deliveroo insists the majority of its riders are happy, as an ITV News investigation reveals the hardship of life for many.
Bavaria is set to roll out a ban of the full-face veil in a number of public places, including schools and universities.