CrowdStrike refutes Delta Air Lines’ allegations that the cybersecurity firm is to blame for a dayslong flight disruption following last month’s catastrophic system outage, saying that the airline rejected repeated offers to help restore impacted systems.

In an interview with CNBC last week, Delta CEO Ed Bastian said the outage cost the company $500 million after more than 6,000 flights were grounded, and that the airline has “no choice” but to seek legal compensation from CrowdStrike and Microsoft.

While the CrowdStrike issues impacted millions of Windows machines across multiple industries globally, Delta struggled to bring systems back online for several days longer than other affected airlines, and is currently being investigated by the US Department of Transportation over how the disruption was handled. Bastian previously said that 40,000 servers had to be manually reset following the outage, noting in a blog post that one of the carrier’s crew tracking-related tools was particularly affected and “unable to effectively process the unprecedented number of changes triggered by the system shutdown.”

CrowdStrike reiterated its apology to Delta in a letter responding to public comments about the airline pursuing legal claims, but said it “strongly rejects any allegation that it was grossly negligent or committed willful misconduct.” CrowdStrike says the litigation threat “has contributed to a misleading narrative that CrowdStrike is responsible for Delta’s IT decisions and response to the outage,” noting that competing airlines restored their operations much more swiftly.

“CrowdStrike’s CEO personally reached out to Delta’s CEO to offer onsite assistance, but received no response,” CrowdStrike lawyer Michael Carlinsky said in the letter. Carlinsky said CrowdStrike had made several other attempts to provide assistance, including an offer for onsite support, but was told that resources for the latter were not required.

“Should Delta pursue this path, Delta will have to explain to the public, its shareholders, and ultimately a jury why CrowdStrike took responsibility for its actions — swiftly, transparently, and constructively — while Delta did not,” said Carlinsky. The letter also notes that CrowdStrike’s contractual liability is capped “in the single-digit millions,” and that the company will “respond aggressively” to litigation “if forced to do so.” We have reached out to Delta for comment and will update this story if we hear back.