common cause

plural common causes

1. countableuncountableA shared purpose.

   And now a common enemy—pollution—promises to press the littoral nations of the Baltic into common cause.

   1989 May, Priit J. Vesilind, “The Baltic: Arena of Power”, in National Geographic, volume 175, number 5, page 605

   1 more example

   An open invite has been given to all UK workers to join in common cause with the union, as more than 40,000 RMT members at Network Rail and 13 train operating companies walked out on June 21 in the first of three 24-hour strikes over pay, conditions and job security.

   2022 June 29, Paul Stephen, “Network News: Strikes set to escalate as RMT issues rallying call”, in RAIL, number 960, page 6

2. countableuncountableUsed other than figuratively or idiomatically: see common, cause.