The deadline for public comments to the FCC over the proposed merger is Monday. Almost 10,000 new comments were received Thursday, bringing the total to almost 52,000.
As the deadline approaches, the deal's sharpest critics and biggest supporters are expected to file their comments. Among the critics could be nonprofit advocacy organizations and content providers such as Netflix and Dish Network.
Mayors outside the region who joined Nutter include those in Orlando; Columbia, S.C.; Stafford, Texas; Attleboro, Mass.; Denver; and Anaheim, Calif.
In Pennsylvania, the mayors of Bensalem, Media, Lancaster, and York support the deal, according to the Nutter letter. The New Jersey mayors of Camden, Bridgeton, Lambertville, and Trenton also signed on.
Absent were the mayors of New York City and Los Angeles, two cities that could be most affected by a Comcast/Time Warner Cable merger. Both of those TV markets are served by Time Warner Cable.
Los Angeles Mayor Eric Garcetti this week asked the FCC to extend the deadline for the public comment period.
"I proudly and enthusiastically support this business transaction because Comcast has always been a great corporate citizen in Philadelphia and I thank my fellow mayors for joining me," Nutter said in his statement. "The merger of Time Warner Cable and Comcast will lead to improved services and increased investment in existing Comcast markets."
When asked whether Comcast had requested the letter of support, Nutter's spokesman, Mark McDonald, said, "I have no idea."
He said that Nutter phoned and e-mailed mayors he knew through the years.
"The call went out widely and what came back came back," McDonald said. Nutter "was pretty pleased with the chief executives from towns all over the country participating."
Comcast officials referred questions regarding the letter to Nutter's office.