Insist on ordering it, plus tea (9)
I believe the answer is:
stipulate
'insist on' is the definition.
(I've seen this before)
'ordering it plus tea' is the wordplay.
'ordering' indicates an anagram.
'it'+'plus'+'tea'='itplustea'
'itplustea' with letters rearranged gives 'STIPULATE'.
(Other definitions for stipulate that I've seen before include "Specify as an essential part" , "Insist on as part of agreement" , "Demand, specify" , "Demand as part of agreement" , "Make a demand" .)