... could result in a hefty fine
.... is unacceptable here
We are obliged to...
Staff must be aware of our code-of-conduct
You must accept that you broke the rules
It's against the rules to....
You must obey the rules
.... is restricted during working hours
.... is a sackable offence
..... is a punishable offence
You will pay the price for insolence
This is not permitted
We are forbidden to....
Staff members are not allowed to....
.... is strictly forbidden/prohibitted
Rules must be obeyed at all times
We must avoid....
.... is banned in the workplace
We recommend that our staff....
You can be fired for....
Staff members are asked/expected to....
Make yourself familiar with company policy
Failure to comply will result in....
Anyone found to be disobeying these rules will be instantly dismissed
It is imortant to...

It is vital that you...
.... is frowned upon
It's not advisable to....