hidden agenda 
noun
A secret or ulterior motive for something: she feels there’s a hidden agenda behind the proposed road...
- He gives much less consideration to the messier aspects of real policymaking - partisan and bureaucratic politics, hidden agendas, ulterior motives, and personal ambition.
- ‘We had no hidden agendas, no secret mission,’ asserts Eugene.
- Exploring hidden agendas behind recent Hollywood films, as well as giving examples of more overtly politically independent film, the collection shows how contemporary American film reflects a diverse range of issues.