JO 7110.65 6-6-2

Assign an altitude to an aircraft only after the aircraft previously at that altitude has reported at or passing through another altitude separated from the first by the appropriate minimum when:

Severe turbulence is reported.

Aircraft are conducting military aerial refueling. REFERENCE-

FAA Order JO 7110.65, Para 9-2-13 , Military Aerial Refueling.

The aircraft previously at the altitude has been: Issued a clearance permitting climb/descent at pilot's discretion.

Cleared to CRUISE (altitude). However, do not use Mode C to effect separation with an aircraft on a cruise clearance. NOTE-

An aircraft assigned a cruise clearance is assigned a block of airspace from the minimum IFR altitude up to and including the assigned cruising altitude, and climb/descent within the block is at pilot's discretion. When the pilot verbally reports leaving an altitude in descent, he/she may not return to that altitude.

REFERENCE-

P/CG Term - Cruise.