Firm backed to pressure US ink producer (7)
I believe the answer is:
octopus
'ink producer' is the definition.
(octopuses secrete ink)
'firm backed to pressure us' is the wordplay.
'firm' becomes 'co' (a firm is a company).
'backed' is a reversal indicator.
'pressure' becomes 'p' (abbreviation).
'co' written backwards gives 'oc'.
'oc'+'to'+'p'+'us'='OCTOPUS'
(Other definitions for octopus that I've seen before include "Influential person" , "Sea creature's tentacles served as food" , "one that's heavily armed?" , "Tentacled, shell-less mollusc" , "fairground ride" .)