The possible strike by Long Island Rail Road workers is going to be a headache for some subway riders as well.

Straphangers already packed into crowded trains are going to have more company if the roughly 5,000 union workers walk off the job at 12:01 a.m. on Sunday.

Part of the MTA's contingency plan to get Long Island commuters -- about 300,000 riders on an average weekday -- to work in the city is to provide shuttle buses that connect to the A line at Kennedy Airport; the No. 7 line at Citi Field-Willets Point; and the M and R lines at Woodhaven Boulevard.

There also are special park-and-rides set up at Citi Field and the Aqueduct Race Track, which have 7,000 parking spaces combined. Subway fares at these locations in the morning will be waived.

"We do know that many of the lines are already maxed out," said Bill Henderson, director of the Permanent Citizens Advisory Committee to the MTA. "There's not a lot you can do as far as adding service and that's going to be a real issue."

The MTA is expecting an increase in ridership on the No. 7, E, A, J, Z, M and R lines. The agency is warning riders to stay away from the "heavily-utilized" E and F lines in Queens and instead try the J and Z lines -- which start their run at Jamaica Center and Archer Avenue -- and the M and R lines.

MTA spokesman Kevin Ortiz said it's unclear if and how the MTA will cross-honor LIRR tickets with New York City Transit.

While there are lines maxed out on the number of scheduled trains that can be run, there will be "gap trains" placed at strategic locations during delays and crowding, like along the Queens Boulevard, No. 7 and A lines, according to Ortiz. "Those gap trains would be popped in to address those situations," Ortiz said.