Sitelinks are a way for advertisers to extend their ads with deeper, more relevant content to searchers in the form of additional links within a text ad. Sitelinks extensions provide up to four extra links to pages within your website versus one link to one landing page from a standard text ad. In addition, Google recently released a new form of sitelinks called Enhanced Sitelinks which includes closely related search ads pulled from your AdWords account.
The search engine has announced that it will begin to strictly enforce its sitelink policy which requires each sitelink within a campaign to direct users to a different landing page. Google said that they have identified advertisers using multiple sitelinks that point to identical URLs within the campaign.
New sitelinks or any changes to existing sitelinks will go through the approval process and the advertising platform will verify that each sitelink has a unique URL. Google says which sitelinks that do not meet the policy will be restricted from showing.
Advertisers are recommended to ensure that destination URLs for sitelinks are unique. Google says that existing sitelinks will not go through the approval process immediately, but will be reviewed within a few months.