LIRR officials say track work this weekend will impact service on the Port Jefferson, Montauk, Oyster Bay, Babylon, Ronkonkoma, Far Rockaway and West Hempstead branches.
The work will be done to put new concrete ties, rail and switch replacements on the Port Jefferson branch.
Riders are being urged to allow extra travel time.
According to officials, the most significant impacts to service will be on the Port Jefferson, Montauk and Oyster Bay branches.