Terms of Service Plugin for WordPress places a checkbox that requires a user to check to proceed.
Terms of Service by WPMUDEV
Easily add a checkbox to your signup process with Terms Of Service for WordPress. You can place the Terms of Service for WordPress on any page.
The TOS for WordPress give you protection by ensuring people acknowledge your Terms before proceeding with the action associated with those terms. For example, if you run a multi-site network and somebody wants to build a site, they will need to agree with your terms, or they won’t be allowed to build a site. The TOS prevents automated spam blog creations too.
Get started with the Terms of Service Plugin for WordPress today.