The mobilization will shut down public and municipal services and paralyze ferries and trains, but flights are unaffected, AFP reported.
Urban transport in Athens will also operate on reduced hours.
Protests are scheduled in Athens and other major cities during the day.
The government has said the 13-hour workday, to be voted into law Wednesday, is optional but opposition parties and unions argue that workers will risk layoffs if they refuse longer hours.
Another general strike on the issue was held October 1.
“This (law) strengthens employees and facilitates businesses,” Labor Minister Niki Kerameus told SKAI TV on Tuesday.
It broadens benefits for working mothers and allows staff to negotiate a four-day working week, she said.
The legal working day in Greece is eight hours, with the possibility of performing paid overtime.
Greece has already legalized a six-day working week, especially during high demand in certain sectors including tourism.