At a tech conference Tuesday, Musk hit out at Bezos for suing NASA to block Musk’s space company, SpaceX, from receiving a $2.9 billion contract to develop a lunar lander that would carry astronauts to the moon. Blue Origin had also bid on the contract, but lost. “I think he should put more of his energy toward getting to orbit than on lawsuits,” Musk said on stage about Bezos, referring to Blue Origin’s recent launch into suborbital flight. “You cannot sue your way to the moon, no matter how good your lawyers are.”

Bezos responded on Wednesday, pointing out that SpaceX also has a history of suing the U.S. government to get its way. “SpaceX has a long track record of suing the U.S. government on procurement matters and protesting various governmental decisions,” a spokesperson for Amazon’s satellite division, Project Kuiper, told Fortune. (The division is developing a broadband Internet satellite constellation akin to SpaceX’s Starlink project.) “It is difficult to reconcile that historical record with their recent position on others filing similar actions.”

The Amazon spokesperson went so far as to provide a document detailing several lawsuits filed by SpaceX against the government and competitors in recent years, as well as numerous protests to both the Government Accountability Office and the Federal Communication Commission. The litigation includes a 2019 complaint against the U.S. Air Force’s decision to overlook SpaceX for launch contracts ultimately awarded to Blue Origin, Orbital Sciences (now a part of Northrop Grumman), and a joint venture between Boeing and Lockheed Martin. Another lawsuit, from 2014, protested the Air Force’s awarding of a sole-source launch contract to the Boeing-Lockheed team, known as United Launch Alliance.

Representatives for SpaceX did not return a request for comment. In a tweet on Wednesday afternoon, Musk addressed Bezos’ rebuttal and attempted to differentiate SpaceX’s approach to litigation from Blue Origin’s. “SpaceX has sued to be *allowed* to compete, BO is suing to stop competition,” Musk wrote.

The feud between the two tech titans started shortly after Blue Origin lost the lunar lander contract in April and then sued NASA over its decision last month. The company claimed in its lawsuit that the space agency had conducted an “unlawful and improper evaluation of proposals,” and is seeking to force NASA to reopen the contract bidding process and “make a new selection and award.”

Yesterday wasn’t the first time that Musk has ribbed Bezos over Blue Origin’s lawsuit. Last month, Musk tweeted that Bezos had retired as Amazon CEO in July “in order to pursue a full-time job filing lawsuits against SpaceX.” Bezos had said he was retiring to focus on various other business and philanthropic endeavors.

The professional rivalry between the world’s two richest men has escalated as each has parlayed their primary business interests—Amazon in Bezos’ case, and Tesla in Musk’s—into ambitious forays in aerospace and space exploration. But the outspoken Musk has been more willing to needle Bezos with public comments—even taking tech journalist Kara Swisher’s bait at the Code Conference on Tuesday to poke fun at the phallic shape of Blue Origin’s New Shepard launch vehicle.

When asked whether the two men communicate, Musk said they don’t “verbally”—but acknowledged that he does “subtweet” Bezos occasionally on Twitter.

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