Hun Sen made the comment at the annual ceremony to mark Jan. 7, 1979, when Vietnamese-backed forces ousted the Khmer Rouge from Phnom Penh.
The illicit economy grew from $650 billion in 2011 to $1.77 trillion in 2015, according to the World Economic Forum.
Drivers interviewed by VOA Khmer said they hope the new law will improve the situation.
Cambodia has around 1,000 active unions, most representing some 700,000 workers in the garment and textile manufacturing sector.
Reminder follows last month incident when an off-duty police officer allegedly shot dead two people and wounded a third in a dispute among neighbors.
Prime Minister Hun Sen will join other Asean leaders for a special meeting with US President Barack Obama in California next month.
Sam Rainsy is in exile abroad, facing a jail sentence if he returns to Cambodia, in a defamation case brought by the president of the ruling Cambodian People’s Party, Heng Samrin.
Vorn Pov, the leader of the organization IDEA, was among 23 people arrested in the January 2014 crackdown.
Authorities have released few details about the deaths, and would not confirm reports of a further two deaths of North Koreans, who were admitted to the hospital.
Cambodian farmers are increasingly growing organic rice and vegetables in some places, but there is no official certification available.
At least five people died in a brutal government crackdown during two days of rioting in January 2014.
Police and other security personnel halted a group of mourners on the outskirts of Phnom Penh Sunday that had planned to hold a Buddhist ceremony for protesters killed in early 2014.