Independent John Finnie said he feared policing in northern Scotland was being "militarised" after discovering officers in armed response vehicles (ARVs) were now routinely carrying sidearms.
The former Northern Constabulary, which was merged into Police Scotland one year ago, had insisted that guns were kept in a locked secure box in the vans and only removed with specific permission from a senior officer.
Assistant Chief Constable Bernie Higgins, the officert in charge of national firearms policy, told former officer Mr Finnie in a letter: "With the creation of Police Scotland the decision was taken to provide a standing authority for a limited number of trained ARV officers to overtly deploy with sidearms and less lethal weapons.
"The reason for this was quite simple - where there is a delay in a firearms officer responding to an incident where there is a firearms threat, then this unnecessarily puts the public and unarmed police officers at greater risk.
"No longer do officers have to stop en-route to an incident and arm themselves, a process that can take anything from 10-20 minutes, they can now deploy directly to a scene and provide that immediate protection. The standing authority also allows them to deal with an immediate threat as a result of an unexpected encounter."
Mr Higgins added that Mr Finnie had suggested the wearing of sidearms by armed response officers appeared to constitute a "militarisation" of policing.
He said this a view he did not agree with, adding: "A key aim of police reform was to provide more equal access to specialist support and national capacity across all areas of the country. This includes firearms assets."
Police sources said it was not the case that armed officers patrol the streets. They are in their ARVs and only come out to deal with emergencies. However, the vehicles can and are also used in support of more routine policing issues, said Mr Finnie. This included supporting officers at the time when the nightclubs are closing and people disperse. This has historically been the case in big cities like Glasgow.
"So, you have armed uniformed officers on the streets of the Highlands for what is routine police business of monitoring crowds leaving licensed premises," said Mr Finnie, a former Police Federation official. "I understand this is uniform practice across Scotland. But routine deployment of armed officers in the Highlands, even in small numbers, is a very worrying development."
The MSP, who plans to raise the matter at Holyrood's Police Committee, said the new policy failed to reflect differences in culture between the Highlands and the rest of Scotland.
He said he would be writing to the Chief Constable of Police Scotland, Sir Stephen House, to remind him the Highlands and Islands is the safest place in the UK.
Mr Finnie said current public support for the police could be threatened by the deployment of armed officers
Chief Secretary to the Treasury Danny Alexander, the LibDem MP for Inverness, Nairn, Badenoch & Strathspey, backed his view, saying there is no need for officers to carry firearms in the region.
He said: "This development is distressing and many Highlanders, myself included, will be shocked by the new police tactics.
"We are lucky to live in one of the safest parts of the UK and the SNP's new centralised police force seems hell bent on bringing anti-riot mounted units and armed police - there is simply no need for officers to carry fire-arms in the Highlands."