Sydney train workers voted to go ahead with a 24-hour strike on Monday, although timetable disruptions will begin on Thursday when workers enact an overtime ban.

It comes after a fortnight of negotiations between the NSW government and the Rail, Tram, and Bus Union (RTBU) which represents more than 6,000 members failed to hammer out an agreement.

"Unfortunately my members have overwhelmingly decided that the offer on the table is nowhere near good enough and our industrial action will continue," said RTBU NSW secretary Alex Claassens.

NSW transport minister Andrew Constance said train service will be cut to a Saturday schedule starting on Thursday and continuing through the Australia Day holiday.