STORY: Le Pen, who lost to French President Emmanuel Macron in last April's presidential elections, will have to run in a runoff because of rules on minimum turnout.
The first round of the legislative vote saw a record abstention of 51.3%, pollsters projected, with voters staying away from polling stations on a hot, sunny Sunday.
Addressing supporters, Le Pen said Macron would abuse any majority "to apply his autocratic and brutal style."
"We risk being in a tunnel for five years, a tunnel without light. For most of the French people, this situation will no longer be bearable," she said.
Macron is not guaranteed to win an absolute majority in parliament, exit polls showed, after a new left-wing alliance, NUPES, made a strong showing in the first round of parliamentary elections on Sunday.
Le Pen called on voters to abstain from voting in constituencies which will see a duel between a candidate with Macron's party and one from the left-wing alliance.