Reissue proceedings cannot be used to withdraw a terminal disclaimer from an issued patent.
A patent issued with a recorded terminal disclaimer. After it issued, the patentee filed a Reissue Application seeking to rescind the terminal disclaimer. The PTO rejected the Reissue Application in part because 35 U.S.C. § 251 “precludes expanding a reissued patent’s term beyond that set when the original patent issued.” (Op. at 6.). The patentee appealed.
The court held that a terminal disclaimer recorded with an issued patent effectively defines the patent’s term. “When a patent issues subject to a terminal disclaimer, the patentee therefore has not just agreed to forgo some amount of its enforceable term, but has in fact reduced the term itself by effectively eliminating the disclaimed portion from the original patent.” (Op. at 11.)
Thus, because the PTO’s reissue authority is limited to the term of the original patent, “[o]nce the  patent issued with the terminal disclaimer in place, and the terminal disclaimer consequently became part of the original patent, the PTO was foreclosed from later reissuing the patent for a term greater than that of the original  patent.” (Op. at 11-12.) As a result, the court affirmed the final judgment of the PTO.
A copy of the opinion can be found here.