Opposed to increases in a toll, initially (7)
I believe the answer is:
against
'opposed to' is the definition.
(I've seen this before)
'increases in a toll initially' is the wordplay.
'increases' becomes 'gains' (gain is a kind of increase).
'in' indicates putting letters inside.
'initially' suggests taking the first letters.
The initial letter of 'toll' is 't'.
'a'+'t'='at'
'gains' placed inside 'at' is 'AGAINST'.
(Other definitions for against that I've seen before include "Opposed" , "on the other side" , "Not supporting" , "Placed in direct contact with" , "In contrast to; touching" .)