“No exceptions!”

You are responsible for processing employees' reimbursement requests at your company. You need for everyone to submit their requests by Dec. 8th, but every month some people try to send theirs after the due date. You don't want them to do this, so in an e-mail you remind everyone of the due date and then write:

No exceptions!

No exceptions!

When you have certain rules that people have to follow, sometimes you let a few people break the rules. For example, when I was a high school teacher, I used to let some students turn in their homework late if they had a good reason why they couldn't finish it in time. Letting people break the rules is called "making an exception".

So when you say "No exceptions" it means that you're not going to let anyone break the rules. In the example above, it means that you won't pay back any employees who send their requests after the due date.