Answer: Schedule PC
Explanation:
Since 2011, Schedule PC has been used for this purpose. It is filed together with form 706 to protect the right to claim an expense that is currently non-deductible or under dispute. If this is due to a limitation such as a time constraint, the claim can be filed by submitting a schedule PC to the IRS. Then when the time requirement has been fulfilled, its duplicate will be submitted to advise about the refund being claimed.