A planned 24-hour train strike later this month could cost the local economy more than $100 million, the Sydney Business Chamber says, labelling the strike "simply outrageous".

Patricia Forsythe, executive director of the Chamber, also said the rail union's call for people to stay home on the day of the planned strike on January 29 was irresponsible.

"It's one of the busiest days of the work year: the Monday after the Australia Day holiday is traditionally one when basically all of the workforce is back from summer holidays, schools are returning. It is a significant day in our economy," she said.

"If they were going to pick a day for maximum disruption they've certainly done that."