The scheduling procedure can be initiated by any State party to the Convention or by INCB. The initiator notifies the Secretary-General of the United Nations of the suggested scheduling change and provides them with supporting information. The Secretary-General then transmits the notification to the State parties, the Commission on Narcotic Drugs (CND) and INCB.
INCB conducts the assessment and makes a scheduling recommendation to the CND. Under article 12 paragraph 4, INCB examines information provided by the States parties and its decision shall reflect:
INCB's scheduling recommendation is voted by the CND. A two-thirds majority (at least 36 Members of the CND) must vote in favor to take a decision to add a substance to, remove it from, or transfer it between the Tables of the 1988 Convention. The Secretary-General then communicates the decision to all States. Decisions enter into force 180 days after the date of such communication.

International scheduling of precursors since 2014. The full history is available here.
Scheduling decisions are subject to review by the ECOSOC upon the request of any State party. The request for review must be filed within 180 days of receipt of notification of the decision. ECOSOC may confirm, alter or reverse the decision of the CND, and the ECOSOC decision is final.
After a scheduling decision becomes effective, State parties should enact national legislation to comply with the provisions of article 12 of the Convention. A number of tools have been made available by INCB to support Governments in their efforts.
The scheduling is a substance-by-substance process. However, the scope of control of the 1988 Convention is extended to salts and (stereo)isomeric forms of certain scheduled precursors, whenever they exist.
CND resolution 65/3 of March 2022 invited INCB and Governments within their respective purviews to consider derivatives and related chemicals which may readily be converted to or used in place of a to-be-scheduled substance.
International control of two additional fentanyl precursors and two groups of amphetamine-type stimulant precursors enters into force (3 December 2024)
INCB takes part in Commission on Narcotic Drugs thematic discussions and reconvened session (8 December 2023)
International Narcotics Control Board recommends scheduling of 18 precursors of fentanyl and amphetamine-type stimulants (28 November 2023)