on pain of

preposition1

1. •
   Used to warn of consequences if a specified act is done or not done: subject to the punishment of (some penalty); or (generally) subject to the circumstance of (some thing).

   • On paine of death, no person be so bold, Or daring, hardy, as to touch the listes, Except the Martiall and such officers Appoynted to direct these faire designes. — 1595