Duty calls American British noun phrase
Used as an exclamation expressing one must cease enjoying something pleasant to turn back work and do a particular task.
Watching TV shows is really tempting, but duty calls, I need to handle all of the emails.
Sorry, I gonna leave the party soon. You know, duty calls, I must go to the hospital for my night shift.
Duty calls, I have to send all documents regarding the meeting to the boss.