Apart from the safety of patients, the source said the police had also taken the step to curb defacement of public property.
The Youth Congress had recently launched a campaign against the pictures of CM Parkash Singh Badal on the ambulances, saying that the funds for the new ambulances had been sanctioned under a Centre-sponsored scheme.
Taking to HT, a police official, who did not wish to be named, said: "We have been given orders not to leave the ambulances for even a minute. The thumb rule is that we have to protect government property from being defaced or attacked."
The driver of one of the ambulances, Gurdiyal Singh, said there was fear that the Youth Congress' campaign could endanger the life of a patient.
Youth Congress worker Deepjyot Kaur said they had launched the campaign as the state government was not ready to carry a picture of the PM on the ambulances. "But we are not going to stop ambulances carrying patients. We are aware of the repercussions," she said, adding that the Youth Congress planned to target stationary ambulances.
In spite of repeated attempts, the superintendent of police was unavailable for comment.