The closure is so workers can complete a major part of the seismic retrofitting of the bridge.
Margena Wade with Caltrans says Labor Day weekend was chosen because traffic is historically lighter than usual:
 
This lets us know that we will be impacting the least amount of people as possible.
 
BART and ferries have extended their service hours, and buses will be allowed on the lower deck about once an hour.
Drivers are advised to take the Golden Gate or the San Mateo bridge for eastbound travel. The upper, westbound deck of the bridge will remain open throughout the weekend.