CrowdStrike Holdings Inc. says the leadership of Delta Air Lines Inc. failed to respond to an offer for assistance in the wake of last month’s catastrophic system outage that led to thousands of canceled flights and a federal investigation of the U.S. carrier.

The allegation, in a letter on August 4 from attorneys for the technology firm, builds upon CrowdStrike’s claim last week that Delta rejected its repeated attempts to help. CrowdStrike said that its chief executive officer, George Kurtz, tried to connect with his counterpart at the airline, Delta CEO Ed Bastian.

“CrowdStrike’s CEO personally reached out to Delta’s CEO to offer onsite assistance, but received no response,” according to the letter, which was signed by Michael Carlinsky, co-managing partner of law firm Quinn Emanuel Urquhart & Sullivan.

In a separate emailed statement, CrowdStrike said that it hopes Delta will “agree to work cooperatively to find a resolution.”

Delta hasn’t any response to the letter from CrowdStrike, a spokesperson said, but drew attention to Bastian’s earlier comments to CNBC that referenced legal action to seek financial relief related to lost revenue, compensation to passengers and reputational impact.

The Atlanta, Georgia-based carrier was by far the worst hit airline as it struggled to normalize flight operations several days after the outage. Delta said it took a $500 million charge after canceling more than 5,500 flights in the several days that followed the initial CrowdStrike outage that impacted computers powered by Microsoft Corp.’s Windows operating system.

In the letter, lawyers for CrowdStrike also pointed out that “any liability by CrowdStrike is contractually capped at an amount in the single-digit millions.”

Spirit Airlines Inc. said the outage that occurred in mid July would contribute to a $7.2 million negative hit to third quarter operating income. Meanwhile, Tony Fernandes, the co-founder of one of Southeast Asia’s largest low-cost carriers, AirAsia, has also demanded compensation for the disruption.