After Friday's endorsement, the law must go to both houses of Parliament for approval.
A government statement says the law is needed to protect the honor and reputation of the monarch.
The 64-year-old King Norodom Sihamoni is a constitutional monarch who maintains a low profile and plays a minimal role in public affairs, while Prime Minister Hun Sen exercises almost absolute control over politics.
Neighboring Thailand has the world's strictest lese majeste law, carrying up to 15 years in prison. Critics say the law is often wielded for political reasons.
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