PARISMillions of French voters headed to the polls Sunday to cast ballots in the first round of parliamentary elections that will determine whether President Emmanuel Macron has a majority to press ahead with his pro-business agenda.

Standing in his way is far-left firebrand Jean-Luc Mlenchon whose party has managed to forge a coalition of French socialists, communists and greens that is rising in the polls. Mr. Macrons party and its allies are still expected to win the most seats after the elections June 19 runoff, according to polls, but he is seen as unlikely to have the commanding majority that allowed him to steamroll the opposition during his first term.