vested interest

noun5

1. •
   A stake, often financial, in a particular outcome.
2. •
   An exceptionally strong interest in protecting or promoting something to one's own advantage.

   • Mr Yates conceded: "These cases are very difficult to prove because they are bargains made in secret. Both parties have an absolute vested interest in those secrets [not] coming out. — 2007
3. •
   [in the plural] A group of people or organizations with such a stake, especially those that seek to control an existing system or activity from which they derive benefit.

   • But it was not a question of evidence, of guilt or innocence. Tom Mooney was bitterly hated by the vested interests of San Francisco. He had to be gotten out of the way. — 1929
4. •
   An indefeasible right or title, distinguished from a contingent interest, which could be defeated (i.e. cease) if a certain event occurred.
5. •
   A fixed right granted to an employee, especially under a pension plan.