Local 159 president Lorenzo North said he had not yet made a decision on whether to appeal again. The award covered an arbitration period that ended earlier this year, and the two sides are in talks over the current period.
The arbitration award, initially issued in 2012, was a bright spot for Nutter in his struggle to reduce the city's long-term pension costs.
It forced new hires of the 2,200-member union to enroll in a "hybrid" pension plan that combines a limited defined-benefit pension with a 401(k)-style investment.
Nutter has been unsuccessful in attempts to get new hires in the city's four largest unions, where employees have a full defined-benefit pension, enrolled in the hybrid plan.
The issue of whether arbitrators should consider the city's ability to pay - established through a law passed during the city's early 1990s financial crisis - has become contentious under Nutter, who has sought to reduce labor costs with the firefighters union through that provision.
State Rep. John Taylor, R-Northeast Philadelphia, introduced a bill this year that would eliminate the clause from that law, the Pennsylvania Intergovernmental Cooperation Authority Act.
Union officials, many of whom have warred with Nutter for years as he sought to cut labor costs during and after the recession, are supporting the bill.
On Twitter: @SeanWalshDN