Teams will be reduced from nine riders to eight for next year's three Grand Tours while the 2018 Tour de France will start a week later to avoid clashing with the soccer World Cup.
The International Cycling Union (UCI) said in a statement on Thursday its Professional Cycling Council (PCC) applied the change which would come into effect in 2018.
In annual running order, the 'Grand Tours' consist of the Giro d'Italia, Tour de France and Vuelta a España.
The move to reduce the size of teams has been on the agenda for some time to make races less predictable and too easy for leading teams to control and also for safety reasons.
"The size of teams taking part in the three Grand Tours will be reduced from the current nine to eight, thereby reducing the peloton size to a maximum of 176 and assisting in efforts to ensure the safety of the peloton and the rest of the race convoy," a UCI statement said.
"It is intended that the maximum peloton size for other races in the UCI WorldTour and the UCI Continental Circuits will also be reduced to 176, with the regulations to put this into effect being submitted for approval in due course.
"These changes will be effective from the 2018 season."
Next year's Tour de France will start on July 7, meaning it will only overlap with the World Cup in Russia by a week.