"In each of the meetings, we emphasized that the exhaustive record before the Commission demonstrates that the takeover would result in substantial harms to consumers, competition, and the public interest and cannot be cured with conditions — it’s unfixable," Keeney wrote in Sprint's filing.
She argued "approval of AT&T’s takeover would harm consumers and tip the wireless industry inexorably toward duopoly."
If the merger is approved, Verizon and AT&T would be the dominant wireless carriers, leaving Sprint a distant third.
Sprint and the Justice Department have both sued to block AT&T's $39 billion acquisition of T-Mobile, alleging that the deal would violate antitrust law by stifling competition in the wireless market. AT&T filed a motion to dismiss Sprint's case on Friday.
The FCC is conducting its own independent review of the deal to determine whether it would serve the public's interest.
In Sprint's FCC filing, the company urged the commission to hold a hearing before an administrative law judge to evaluate the merger if it chooses not to block it outright.
AT&T argues an administrative hearing is unnecessary.
“The FCC has indicated that it is continuing its review of the voluminous data it has amassed in the record of the proceeding," an AT&T spokesman said. "There is no legal or policy reason to designate the proceeding for a hearing.”
—This story was updated at 12:23 p.m.