The Quebec transport ministry said in an advisory that the complete closure of Route 138 East is necessary "because of connecting work to the new Monette Bridge in LaSalle."
"No traffic will be allowed towards Montreal on the Honoré-Mercier Bridge," the advisory said.
The closure will be in effect until Friday 5 a.m.
Drivers should be ready for a detour.
"You'd have to take the Champlain Bridge or take the 30 and go through Valleyfield if you want to head towards the West Island," said CBC Radio One traffic reporter Jennifer Allen, adding that the overnight closure could cause delays on other spans.
"This may cause congestion at the Champlain Bridge."