A row has broken out over advice given to police in England and Wales telling them not to stop and search people only because they smell of cannabis.
It was first given to police last year and was reiterated by an Inspectorate of Constabulary report on Tuesday.
The advice says officers should look at other factors like behaviour as well.
But some officers, including the chief constable of Merseyside Police, said they disagreed. The College of Policing said it plans to review the guidance.
Police officers can use stop-and-search powers if they have "reasonable grounds" to suspect someone is carrying items such as drugs, weapons or stolen property.
Last year, they were given new guidance by the College of Policing that the smell of cannabis on its own would not normally justify stopping and searching someone or their vehicle.
But the Inspectorate of Constabulary said many officers were unaware of the guidance and it is now urging forces to encourage officers to not rely on a smell alone.
However, Chief Constable Andy Cooke, of Merseyside Police, said he would not be giving that advice to his teams.
He tweeted: "I disagree. The guidance in my view is wrong and the law does not preclude it.
"Smell of cannabis is sufficient to stop search and I will continue to encourage my officers to use it particularly on those criminals who are engaged in serious and organised crime."
Matt Locke, of Northumbria Police, described the guidance as "inconsistent", adding that it was "a bit of a dog's dinner".
Sir, Stop & Search NCALT training from the @CollegeofPolice "The smell of cannabis alone is NOT sufficient grounds to justify a search". Apparently it's not an offence to be in possession of the smell of cannabis. #whoknew pic.twitter.com/IDEVEAsaoz— Matt Locke (@Im_Locky) December 12, 2017
Another police officer, from North Yorkshire Police, tweeted: "If I smell cannabis on someone or coming from a vehicle then I'll conduct a search. I don't think there's a cop in this land that wouldn't.
"Recently not only had that led to me seizing quantities of cannabis, but also arresting drivers showing with it in their system."
Sorry but even as a trainer I'm confused 😐 "strong smell of cannabis" would give me reasonable grounds to suspect a person is in possession of cannabis?! I can't see how a "strong smell" would be from clothing alone? A faint smell is a bit different!— Josh Bourne (@JoshBourne9) December 12, 2017
Mike Cunningham, HM Inspector of Constabulary, responded to questions on social media about the guidance by saying the smell of cannabis "can be reasonable grounds" to search but it will be "for the officer to explain".
He added that the advice "encourages multiple grounds" to merit a stop and search.
The row came after the Inspectorate of Constabulary analysed more than 8,500 stop and search records and found almost 600 were conducted solely because police could smell cannabis.
Searches based on other grounds, such as the suspect's behaviour, result in more arrests, the report said.
Analysis: By Danny Shaw, BBC home affairs correspondent
At the heart of this row is an important question: are too many people being needlessly stopped and searched for drugs?
The Inspectorate report drops a heavy hint that they are.
It says police carried out 3,698 searches, 43% of the sample, because officers believed a suspect had drugs on them for their own use, even though drug possession offences may not be "priority crimes".
The watchdog is concerned about this, firstly, because drug possession searches are not necessarily the best use of police time; and secondly, because they appear to affect ethnic minority groups disproportionately.
That's one of the key reasons why the Inspectorate has reinforced the College of Policing guidance on stop and searches, including the advice about smelling cannabis - even though it's caused a stink.
No one likes a stink!— College of Policing (@CollegeofPolice) December 12, 2017
We’ve plans to review the guidance on whether the smell of cannabis on its own is sufficient grounds for a stop search. We encourage multiple grounds for a stop search but officers can, and do, use their judgement. https://t.co/FzLCXtVEFi
The report said it was "troubling" that black people were eight times more likely to be stopped than white people.
At the same time, black people were less likely to have illegal substances found on them than white people.
The National Police Chiefs' Council said it was looking at why young black men were disproportionately stopped.
The NPCC said stop-and-search powers were important "with rising knife and gun crime", as well as being a deterrent for people considering carrying out acid attacks.