The group of armed men must have identified the people before they were shot dead.
“At least 22 people were killed and five injured when militiamen stopped several buses, trucks and vans on a highway,” a local government spokesman told AFP.
The incident is said to have occurred in the Musakhail district of Balochistan province during the night of Monday local time.
The majority of those killed are said to be workers from the Punjab region, which lies between Pakistan and India.
No one has claimed responsibility for the attack, but a separatist group in Baluchistan, which is banned in the country, earlier urged people to stay off the highways, AP writes.