The men were armed with knives when they threatened the staff at the Old Toll Garage in Overtown, near Wishaw.
Det Insp Kenny Dalrymple said one 36-year-old women was hurt when she tried to stop the robbery on Monday night, while her 18-year-old colleague was physically restrained by the men.
"It was a very, very frightening experience for them both," he said.
The men fled the petrol station with a three-figure sum of money and some cigarettes.
Police are appealing for information from anyone who was in the area when the incident took place, at about 22:35.
Det Insp Kenny Dalrymple said: "This attack was obviously planned.
"The suspects waited until nearly closing time, possibly hoping to get the days' takings and maximise their haul, however, they were thwarted by the staff, one of whom (a 36-year-old woman) sustained a cut to her shoulder as she tried to stop the robbery.
"The other woman, aged 18 years, was restrained by the men during the attack, but was otherwise uninjured.
"Both were treated by paramedics at the scene and did not require to go to hospital, however, this was a very, very frightening experience for them both."
He added: "Officers are currently checking CCTV from the scene and have spoken to people who were on the forecourt at the time of the attack, however, we are keen to hear from anyone who was in the area at the time, particularly any passing motorist who may have dash-cam footage"
Both men were white and about 5ft 7in tall. They were wearing dark clothing and balaclavas or similar face coverings.
Police are hunting for two masked men who attacked two women during a robbery on a petrol station.