I believe this is the oath that your ancestor refused to sign. It was known as the Voter Registration Act of 1867. It stated that all white men age 21 and over were to report to their local Federal military post and sign this oath, which gave them citizenship and the right to vote. The photo is the oath my ancestor signed.

http://i1132.photobucket.com/albums/m574/modie1165/Oath/WMS-1867VotersRegistrationOath.jpg