Long Island Rail Road's ban on platform smoking begins on Sunday.
The Metropolitan Transportation Authority voted in September to prohibit smoking in most outdoor areas of LIRR stations.
For now, those who disregard the ban will get off with a warning.
The MTA told Newsday it's not clear when the grace period will end. When it does, violators will face $50 fines and up to 30 days in jail.
The new policy complies with a new state law signed in August prohibiting smoking at outdoor "ticketing, boarding or platform areas'' of the MTA's two commuter railroads -- the LIRR and Metro-North Railroad.