A man impersonating an attendant at a Uniondale gas station Monday morning took the $20 a woman handed him for gas and ran, Nassau police said, then pulled a switchblade on her male passenger when he tried to get the money back.

First Squad detectives are investigating the 10:30 a.m. incident at Shamrock Gas, 940 Nassau Blvd. as a robbery.

The man was in his early 50s, 6 feet tall and 180 pounds, police said.

Police said the male passenger took the wheel of the vehicle and caught up to the suspect on nearby Pine Street. When he asked for the money back, the man brandished his knife and denied taking anything.

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The victim retreated to the gas station and called police.

Detectives ask anyone with information regarding this crime to contact Crime Stoppers at 800-244-TIPS. All callers will remain anonymous.