Quebec's chief electoral officer is encouraging Quebecers in four ridings to vote on Monday.
There are 215,000 eligible voters in the ridings of Arthabaska, St-Jerome, Verdun, and Marie Victorin.
In Verdun, Former Liberal minister Jacques Daoust was forced to resign because of a controversy over the sale of Quebec hardware chain Rona to American interests.
In St-Jerome, former PQ leader Pierre Karl Peladeau suddenly resigned for family reasons.
In Marie-Victorin, PQ MNA Bernard Drainville quit shortly after Peladeau's resignation.
In Arthabaska, independent MNA Sylvie Roy died from a sudden illness.
The PQ is hoping to hang on to St-Jerome, considered a swing riding.
The CAQ won the riding before Peladeau won it for the PQ, but he didn't win it by a big margin.
Turnouts for byelections are usually lower than general elections.
- With files from CTV News