Amazon founder Jeff Bezos and the Tesla CEO appear to have had a feud rumbling on for years, driven largely by competition to win the commercial race to space.

Last year Amazon announced the biggest rocket deal in the commercial space sector’s history. Amazon was offering contracts for Project Kuiper—a chance to launch low-Earth-orbit satellites which would be used for internet services.

The project, which Amazon confirmed it will invest $10 billion in, signed up three contractors—the United Launch Alliance (ULA), a joint venture of Boeing and Lockheed Martin; European company Arianespace; and Blue Origin, a private venture founded by Bezos himself.

But missing from the lineup is Musk-founded SpaceX, which has reportedly already launched approximately 5,000 internet satellites since 2019 for its own rival service, Starlink.

But despite it being a direct competitor, Amazon shareholder Cleveland Bakers and Teamsters Pension Fund (CB&T) have filed a complaint against Bezos and the board of the online giant—for not appropriately vetting SpaceX as a viable option for Project Kuiper.

The filing emphasizes the rivalry between Bezos and Musk, even featuring screenshots of posts on X—formerly Twitter—where the pair have taunted each other over various space expeditions, CNBC reports.

The filing reportedly adds Amazon executives—including current CEO Andy Jassy—“consciously and intentionally breached their most basic fiduciary responsibilities” by awarding the work to the trio and disregarding SpaceX in the proceedings.

The filing adds Amazon’s leadership “excluded the most obvious and affordable launch provider, SpaceX, from its procurement process because of Bezos’s personal rivalry with Musk,” per CNBC.

“Bezos, it must be assumed, could not swallow his pride to seek his bitter rival’s help to launch Amazon’s satellites,” the suit reportedly adds.

Amazon has dismissed the lawsuit. A spokesperson for the company told Fortune: “The claims in this lawsuit are completely without merit, and we look forward to showing that through the legal process.”

It is unclear whether SpaceX even submitted a bid for the work, or expressed any interest in helping a rival service launch its own satellites.

The company did not immediately respond to Fortune‘s request for comment.

Bezos and Blue Origin

The filing also reportedly takes aim at Bezos’s proximity to both Amazon and Blue Origin, saying there was a “glaring conflict of interest.”

Bezos still sits as the chairman of the board at Amazon having founded the company in 1994, and launched Blue Origin six years later.

According to CNBC, CB&T alleges Amazon’s audit committee only received “a brief summary of the terms of the contracts” before “rubberstamp[ing]” the deal after only a matter of minutes of discussion.

It adds the committee “had no information about how Bezos and his management team conducted the negotiations with Blue Origin. It had no information about the level of Bezos’ involvement. It had no information about how many other launch providers (if any) Bezos and his management team explored contracting with.”

It also highlights apparent issues with Blue Origin contracts in the past—reports surfaced in February that one of the company’s New Glenn rockets had exploded in testing, which is earmarked to be one of the landers for a $3.4 billion NASA project.

Musk vs Bezos

It might be difficult for Musk to keep track of which tech titans he’s feuding with, as there are quite a few.

In recent years he’s challenged Meta CEO Mark Zuckerberg to a physical fight, has called Microsoft cofounder Bill Gates a “knucklehead,” and gotten called a “jerk” by OpenAI’s Sam Altman.

Musk has also fired shots at Apple CEO Tim Cook. As well as implying the iPhone maker is “biased,” Musk posted in November last year: “Apple has threatened to withhold Twitter from its App Store, but won’t tell us why.”

Cook responded in a GQ interview: “[My] philosophy is engagement.”

However, Bezos is one of Musk’s longest-standing rivals, with the latter even calling for Amazon to be broken up—claiming it is a “monopoly.”

The duo’s space race rivalry has also been a point of contention.

Congrats @SpaceX on landing Falcon's suborbital booster stage. Welcome to the club!

— Jeff Bezos (@JeffBezos) December 22, 2015

Musk has accused Bezos of being a copycat after news broke that Amazon was looking to launch its Starlink rival.

Maybe it’s a coincidence 🤷‍♂️

— Elon Musk (@elonmusk) December 18, 2022

The richest man in the world also previously said Bezos had “retired in order to pursue a full-time job filing lawsuits against SpaceX” and later told Bezos he can’t “sue [his] way to the moon.”