Restaurant Brands has agreed a deal with the Unite Union, under which workers' hours and shifts will be guaranteed on a permanent basis.
The company operates KFC, Pizza Hut, Carl's Jr, and Starbucks stores.
Together, they have more than 4000 staff - more than half of whom were members of the Unite Union.
The new collective agreement moves from a formula in which hours were guaranteed at 80 per cent of those worked in the previous three months, to one in which all hours are guaranteed and shifts will be fixed.
Unite national secretary, Gerard Hehir, called it a "massive win'' for employees.
Hehir said it was the first time in decades that workers in the fast food industry here would have permanently fixed shifts.
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"No longer will their pay vary from week to week.
"As shifts become available - which happens frequently with staff turnover - workers will be able to build up their hours to the maximum they want to work each week,'' he said.
"Employees will also be offered additional shifts when they become available up to a maximum of 40 hours a week, allowing the opportunity to build up stable, secure full-time employment."
Shares in Restaurant Brands fell 0.2 per cent, or 1 cent, to five-dollars 70. But they are still up 29 per cent since the start of the year.