FCC spokeswoman Janice Wise had no comment on Garcetti's request.
So far, almost 43,000 public comments from TV viewers, civic organizations, and politicians have been filed with the FCC, according to the agency's website.
Thousands of those comments involve apparent fears by TV viewers that Comcast will take RFD-TV, a rural-focused TV network, off cable. The network has asked its viewers to protest.
Other comments opposing the acquisition, in sometimes tart language, delve into high bills and poor customer service by Comcast and Time Warner Cable.
Deal supporters include the Chicagoland Chamber of Commerce, the Associated Black Charities of Baltimore, the Urban Affairs Coalition in Philadelphia, affiliates of the Boys and Girls Clubs of America in the New England area, and the Public Education and Business Coalition in Denver.
About a dozen towns in Upstate New York, in Tompkins County in the Finger Lakes area, say they can't support the deal because of long-running cable-franchise negotiations with Time Warner Cable.
"Time Warner has been extremely difficult to deal with," said Herb Engman, supervisor in Ithaca. Some municipalities have not had new franchise agreements with Time Warner Cable since the 1980s, he said.
"These cable companies have to get their act together before we have an even bigger one," he said.
Time Warner Cable has been more responsive recently during the merger review, but Ithaca still doesn't have a deal, Engman said.
Also filing with concerns about the merger was the California Emerging Technology Fund, a nonprofit organization funded through earlier telecom mergers in the state.
The organization has said that Comcast's Internet Essentials for low-income families needs to be expanded to serve more people. The program is restricted to low-income families with school-age children but should include all low-income families, the group said.
Experts expect more filers near the deadline.
Dish Network, one of the nation's largest pay-TV operators, opposed the deal in meetings with FCC staff and during a congressional hearing in Washington.
Several organizations or companies agreed to confidentiality agreements to access non-public information related to the proposed acquisition.
They include the American Cable Association, Broadview Networks, Cogent Communications Holdings Inc., the Consumer Federation of America, Free Press, the NBC-TV affiliates, Netflix, RCN, the Greenlining Institute, and the Writers Guild of America, West.
Comcast has until Sept. 23 to respond to the comments.