NY Mayor Bill de Blasio and Chicago Mayor Rahm Emanuel are leading the charge. 

Via Guns.com:

In their meeting in Miami this week, the U.S. Conference of Mayors adopted a resolution opposing legislation to recognize concealed carry permits nationwide.

The group’s agenda going into the meeting included a pledge to develop a consensus around gun safety and gun violence initiatives and, in a move backed by New York City Mayor Bill de Blasio and Chicago’s Rahm Emanuel, called on Congress to protect cities from “the threat” of concealed carry reciprocity legislation.

“Such legislation is dangerous as it would damage state and local governments’ ability to craft gun laws appropriate to their needs; and…the goals of this legislation are completely antithetical to all of the efforts to reduce and prevent gun violence,” says the adopted resolution.

The conference, formed of 1,049 mayors of towns and cities with a population larger than 30,000, oppose House H.R. 38 and Senate S.446, which would essentially allow anyone with a valid carry permit to use it in any city, and potentially allowing some to carry that in some circumstance do not meet local requirements.

Read more here.