It follows the collapse of a railway bridge over Abakan River in the Khakas region that was used to deliver raw materials to the two smelters.
About 20kt is expected to be reduced which Rusal said would be reallocated to other smelters.
After the bridge collapsed in early May the smelters started to use automotive transportation for raw material supply.
But it decided automotive freight traffic volume was not sufficient for the needs of the smelters so the decision was taken to temporary reduce the production at both plants and compensate it by reallocation to other smelters.
Work has begun on a temporary rail bridge on the spot of the collapsed bridge near Kamyshta railway station. The bridge is set to be rebuilt in June.
The situation may lead to decrease of the company's aluminium production forecast for the year.