There is no built-in support in ILLiad for enforcing policy agreements, but with the new expired user features added in ILLiad 9. Users should be able to customize an ExpiredUsers.html page to include a policy check box and make it a required field. That way users will not be able to renew their ILLiad account and use the system without checking that required box. The same check box requirement could be done on the new user registration form.
Please see Automatic Expiration of Users for more information.