Verizon has since said it will change its policies for public safety departments during emergencies.
The revelations, which were first reported by Ars Technica, are buried in an addendum to a brief filed in support of 21 states and the District of Columbia, which together filed a lawsuit this year that essentially seeks to restore rules known as net neutrality.
Firefighters monitor a back fire as they battle the Mendocino Complex fire, August 7, 2018 near Lodoga, California.
The company will also be releasing a new unlimited data plan for first responders.
Santa Clara County Fire Capt. Bill Murphy told CNN that the department's connection speed dropped to what you would expect from a dial-up service, making simple tasks like sending an email or updating a Google document nearly impossible.
Verizon officials said this week, however, the slowdown had nothing to do with net neutrality rules, but occurred because the department had exceeded its allotted amount of high-speed wireless data included in its service plan.
The Santa Clara County Fire Department says Verizon slowed its internet communications at a wildfire command centre three weeks ago, crippling the emergency communications truck's data speeds and forcing firefighters to use other agencies' internet connections and their personal cellphones.
"We had a process failure", Erwin said during an interview with IWCE's Urgent Communications.
'In this situation, we should have lifted the speed restriction when our customer reached out to us.
Santa Clara County Fire Chief Anthony Bowden says the throttling made it hard for crews to coordinate during the initial fire fight.
'Verizon imposed these limitations despite being informed that throttling was actively impeding County Fire's ability to provide crisis-response and essential emergency services, ' he added.
Murphy said that firefighters were able to work around the problem by using their own devices, but he is concerned about what will happen if others see their data throttled during an emergency. "For that, we are truly sorry".
The Mendocino fire which began on July 27 has consumed almost 407,000 acres, or roughly half the size of Rhode Island, and as of Wednesday it was 74 per cent contained.
U.S. telco Verizon cut back data service to a mobile command and control centre to just 0.5% of normal level after the firefighters exceeded their data package.
"It's apples and oranges", said Rudy Reyes, Verizon's assistant general counsel in the western USA region.