Tenn. Code § 8-3510
After the time mentioned in § 8-3452, a disability beneficiary restored to active service, at a salary less than the average compensation upon the basis of which he was retired, shall not become a member of the retirement system unless and until such salary is increased to an amount equal to or greater than the average compensation upon the basis of which he was retired on a disability allowance.
Should any disability beneficiary under his minimum service retirement age be restored to service at a salary equal to or greater than his average compensation upon the basis of which he was retired, his retirement allowance shall cease, he shall again become a member of the retirement system and may elect either class A or class B membership unless he previously was a class A member in which case he shall become a class A member. Any prior service certificate on the basis of which his service was computed at the time of his retirement shall be restored to full force and effect, and in addition upon his subsequent retirement he shall be credited with all of his service as a member, but his retirement allowance payable prior to his minimum retirement age shall not be less than the retirement allowance payable prior to his restoration to service and if he is restored to active service on or after the attainment of the age of fifty (50) years, his retirement allowance upon subsequent retirement shall not exceed the sum of the retirement allowance which he was receiving immediately prior to his last restoration and the retirement allowance that he would have received on account of his service since his last restoration had he entered service at the time as a new entrant.
Until such time as this section becomes effective as provided in § 8-3452, § 8-3510 of the Tennessee Code as enacted by chapter 6 of the Public Acts of 1955, prior to amendment, shall remain in full force and effect.
T.C.A. § 8-3510