The Mercier Bridge will be down to one lane in each direction over the weekend.
Workers will be repairing structural elements on the underside of the southbound span.
All traffic will be channeled on to the inbound side between 3 o'clock on Saturday morning and five o'clock on Monday morning. Plans could change, however, if the weather does not cooperate.
Motorists accessing the bridge from La Prairie will find the usual on-ramp closed. They will be directed to a U-turn at Blind Ladies Hill Road.
Bridge officials say more work is planned for the weekends of May 9 to 12 and June 6 to June 9.