Permission for relationship but not for select is possible?

I would like to have two schemas:

MyDB.sales
MyDB.security

Users that have rights in sales schema should be able to
select/insert/update/delete. The same users must have rights to check
foreign keys against users table (but they are now allowed to execute
select on this table).
Is that possible? Can you help me to find relevant page in manuals for
9.1 or 9.2?

I wish to you all a Happy New Year!

Thanks,

Edson