open-door policy

Short definition from Wiktionary

Noun

1. 1
   A policy or usual practice, by a person in authority, of permitting subordinates or constituents to visit his or her office unannounced and at any reasonable time for the purpose of discussing matters of concern.
2. 2
   A governmental policy of encouraging immigration or of permitting increased access by foreigners for purposes of tourism, trade, investment, etc.
3. 3
   Alternative form of open-door policy.