Commissioners unanimously agreed last month with a recommendation from staff members to begin the third phase of the downtown waterline project starting Monday and to try to have it completed by Sept. 7.

The project will limit traffic to one way on parts of Massachusetts Street and temporarily remove significant amounts of parking. This year’s work will affect the 900, 1000 and 1100 blocks of Massachusetts Street.

Staff members previously had discussed the project with several downtown merchants, who were in agreement with the timeline.