Business groups and unions are trashing Mayor de Blasio for holding secret meetings about overhauling private waste pickup.

They argue the city is moving to implement a zone-based system for the private carting industry behind closed doors.

The group says the city’s advisory board should open meetings to the public.

Sanitation Department spokesman Vito Turso said: “This will continue to be… [an] undertaking that achieves the environmental and quality-of-life benefits while prioritizing… service… and… low pricing to customers.”