"If approved, the merger would have serious repercussions around the country," the letter states. "The Commission should not consider this merger without seeking direct input from those most impacted."
Update: An AT&T spokesman responded to the groups' request via email on Tuesday afternoon with a statement citing AT&T's commitment to deploy next-generation wireless broadband to 98 percent of the nation once the merger is approved.
"The FCC has received extensive public comment on this transaction as well as more than a million pages of documents. And while the formal pleading cycle is closed, interested members of the public continue to make their views known in filings at the FCC."
The length of the review and number of conditions attached to the NBC-Comcast deal drew criticism of its own from Republicans and industry, who argued the Commission went beyond its duty to ensure the transaction wouldn't adversely affect competition in related markets.
House Energy and Commerce Telecom subpanel chairman Greg Walden (R-Ore.) is currently drafting legislation that would reform processes at the FCC and institute a shot clock for merger reviews such as AT&T/T-Mobile so they can't extend indefinitely.
Full committee ranking member Henry Waxman (D-Calif.) criticized the effort, arguing Republicans are trying to make procedural changes for political reasons and suggesting the bill is a reaction to the conditions imposed on Comcast as part of the merger.
This post was updated at 4:44 p.m.