Delta Air Lines (DAL.US) has filed a claim against CrowdStrike (CRWD.US) for ignoring assistance during a dual engine failure.

CrowdStrike(CRWD.US) responded to Delta(DAL.US) after its leadership failed to respond to offers of assistance following the disastrous system failure last month that led to thousands of cancelled flights and a federal investigation of the U.S. airline.

The tech company's lawyers made the claim in a letter Sunday based on CrowdStrike's statement last week that Delta rejected its repeated attempts to help. CrowdStrike said its chief executive George Kurtz had tried to contact the airline's chief executive Ed Bastian.

The letter, signed by Quinn Emanuel Urquhart & Sullivan managing partner Michael Carlinsky, said: "CrowdStrike's chief executive personally contacted Delta's chief executive to offer on-site assistance, but received no response."

CrowdStrike said in another email statement that it hoped Delta "would agree to cooperate to find a solution."

Bastian previously said Delta could face up to $500 million in losses from the global IT outage, which included not only direct revenue declines but also millions of dollars in compensation and hotel bills the company had to pay during the five-day service disruption.

With the IT failure, Delta canceled more than 5,000 flights in five days, more than the total number of cancellations in 2019. Bastian said the company had to manually reset 40,000 computers because most of the affected computers had to be fixed manually.

Because Delta's recovery was slower than other U.S. airlines, it even prompted a federal investigation.

Bastian told the media last week that the company was seeking damages for the outage, "we had no choice." He added in a July 31 interview that CrowdStrike had not yet offered any financial assistance, only free consulting.

Delta did not immediately comment outside of normal business hours.