A subway rider was asked to stop smoking on a Manhattan A train Tuesday, prompting him to pull a box cutter and slash two people — one on the ankle and the other their face, cops said.

The incident happened around 2:25 p.m. aboard a southbound A train that was approaching the Canal Street station, according to police.

A 51-year-old man had been puffing away on a lit cigarette when the two victims, 67 and 49 — both males — asked him to put it out. He responded by brandishing the box cutter and attacking the pair, cops said.

One of them men got slashed on his face and the other on his ankle. They were treated at Bellevue Hospital for their injuries and were expected to survive.

The smoker was taken into custody and charges were pending Tuesday night.