The incident happened Tuesday around 7:30 p.m. inside the Union Street subway station on the R train platform.
The 28-year-old victim was attacked by a male and female suspect.
The victim was struck in the head and body before they took her cellphone and threw it on the ground.
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Police say they then sprayed the victim in the face with an unknown liquid.
The victim was taken to the hospital for pain and bruising but is said to be stable.
The suspects ran away in an unknown direction.
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The MTA started enforcing its new mask policy on trains and buses Monday, meaning not wearing a face covering is now punishable with a $50 fine.
The new rule applies to subways, buses and all LIRR and Metro North trains.
Anyone with information is asked to call the NYPD's Crime Stoppers Hotline at 1-800-577-TIPS (8477) or for Spanish, 1-888-57-PISTA (74782).
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