The phrase "prior permission" means that you need to ask for and receive approval beforehand, before you can proceed with doing something. Full definition
No friends or relatives are allowed to stay with yoga students without prior permission from the management. (rishikulyogshala.org)
Some airlines, however, permit small animals in the cabin with prior permission. (si.com)
• The Scottish parliament will also have new powers to make discretionary payments in any area of welfare without the need to obtain prior permission from department for work and pensions. (theguardian.com)