A Northern California fire chief said efforts to battle the largest wildfire in the state’s history were hampered by Verizon Communications Inc., which throttled the fire department’s mobile-data plan to the point that it made communications impossible.

“County Fire has experienced throttling by its ISP, Verizon,” Santa Clara County Fire Chief Anthony Bowden wrote in a court filing first reported by Ars Technica on Tuesday. “This throttling has had a significant impact on our ability to provide emergency services. Verizon imposed these limitations despite being informed that throttling was actively impeding County Fire’s ability to provide crisis-response and essential emergency services.”

The court document was filed as an addendum to a lawsuit filed by 22 state attorneys general seeking to reinstate federal net neutrality rules.

According to the filing, the fire department’s mobile-data plan was severely throttled after it surpassed its monthly data allowance while fighting the massive Mendocino Complex fire north of San Francisco. “Data rates had been reduced to 1/200, or less, than the previous speeds,” Bowden wrote. That impeded their efforts to communicate so much that firefighters were forced to use other departments’ ISPs, or their own personal mobile devices, he said.

When the department complained, “Verizon representatives confirmed the throttling, but rather than restoring us to an essential data transfer speed, they indicated that County Fire would have to switch to a new data plan at more than twice the cost, and they would only remove throttling after we contacted the department that handles billing and switched to the new data plan,” Bowden wrote.

The department eventually did upgrade to a new, more expensive plan.

Bowden said Verizon has throttled data during previous fires, and wrote: “It is likely that Verizon will continue to use the exigent nature of public safety emergencies and catastrophic events to coerce public agencies into higher-cost plans, ultimately paying significantly more for mission-critical service — even if that means risking harm to public safety during negotiations.”

In a statement to Ars Technica, Verizon VZ, -0.17% admitted that the fire department’s data throttling should have been lifted because of the emergency situation, and blamed it on “a customer service mistake.” The company pledged to fix such issues going forward.

While the data throttling was not a direct cause of the net-neutrality repeal, customers now have fewer means of recourse to reverse such actions, and more limited ways to complain.

Verizon shares are up 3.7% this year, compared to the 4.5% gain by the Dow Jones Industrial Average DJIA, +0.98% , of which it is a component.

More than 3,500 firefighters are still battling the Mendocino Complex fire, which has grown to more than 400,000 acres — about half the size of Rhode Island. One firefighter has been killed.