Hezbollah set up checkpoints and started inspecting cars traveling through southern Beirut neighborhoods. A car bomb exploded in the Hezbollah stronghold last week, killing at least 20 people.
The pro-Western Future Movement in the Lebanese Parliament said Hezbollah should reconsider its position on independent security measures in the capital city.
"The militia-like security measures that Hezbollah began implementing in the southern suburbs [of Beirut] and some areas in the south and the Beqaa [Valley] under the pretext of combating terrorist acts are unacceptable measures," a Future Movement statement published Wednesday by The Daily Star newspaper read.
Hezbollah holds political office in Lebanon. Its military wing was designated by the European Union as a terrorist organization.
The pro-Western movement said Hezbollah's actions were "an aggression against the state."
Hezbollah Secretary-General Hassan Nasrallah took credit last week for an explosion along the southern border that wounded four Israeli soldiers.
Hezbollah's role in the Syrian civil war has sparked political divisions in Lebanon. Supporters say its weapons are needed to defend against Israeli aggression, while its opponents say an armed resistance forces Israel to adopt a defensive posture.