The latest in a string of policy updates from Google for Nonprofits requires Google Grantees who have been in the program longer than six months to submit updated nonprofit status documentation for review.
This is just so that Google knows you are still an actual registered nonprofit and that you're following the AdWords guidelines, and it shouldn't require much effort on your part.
Just like the new Google for Nonprofits URL policy, this change will take effect next month and you will have a three-week window to submit a renewal form. Make sure you're following the new URL policy of promoting just one URL before you submit your renewal. They will be checking to make sure you're following all the rules!
Check out the FAQs on the Google Grants page for more details on the renewal policy.