Checkbox before posting: Read and accepted Terms of Use

Hello,

I am searching for a plugin, that inserts a Box, that have to be checked before Saving/Publishing.
I need this, because we have a lot of authors, who have to accept the terms of use before publishing something.

Is something like that available or can someone give me some information, how to write a plugin like this. (I never wrote a plugin for the admin section…)

Thank you in advance,
Kai