The Britain-based Syrian Observatory for Human Rights reported intense clashes between troops and army defectors in the villages of Dael and Hirak in the province of Daraa, where the uprising started. The group also said explosions were heard in the village of Khirbet Ghazaleh and Naima as well as the provincial capital, Daraa.
The Observatory and other activist groups reported violence in several areas including Idlib, Homs and the eastern province of Deir el-Zour.
The two main umbrella opposition groups, the Syrian National Council and the National Coordination Body for Democratic Change in Syria, have called for a boycott. Other groups have called for a general strike.
"I am boycotting the vote," Syria-based activist Mustafa Osso told The Associated Press by phone. He added that previous "reforms" have made little difference. Assad's government revoked the country's official state of emergency in April, but the crackdown on dissent has only intensified.