WASHINGTON — Boeing, enmeshed in a long-running legal dispute with its Russian and Ukrainian partners in Sea Launch, has filed a motion in U.S. federal court to block an impending sale of the launch company by the Russian government.

In a motion for a preliminary injunction filed with the U.S. District Court for the Central District of California April 2, Boeing argued that a sale of Sea Launch could hinder its ability to collect on a summary judgment issued last year against Energia of at least $300 million.

“If Energia succeeds in selling these assets and moving all of the proceeds thereof to Russia, without paying the hundreds of millions of dollars that it owes, it would unquestionably complicate Boeing’s collection efforts,” the company’s lawyers stated in the court filing.

Boeing filed the motion after recent reports that Roscosmos, the Russian state space corporation that holds a controlling stake in Energia, has sold Sea Launch to an unnamed investor.

“I cannot name the investor or disclose the value of the contract by virtue of certain circumstances. I do hope I will be able to say more by the end of April,” Igor Komarov, head of Roscosmos, told the Russian news agency Tass in a March 30 article. Komarov claimed that investors from several countries, including Australia, China, Europe and the U.S., had bid on Sea Launch.

Boeing filed suit in federal court in February 2013, arguing that its Russian and Ukrainian partners in Sea Launch, Energia and Yuzhnoye, refused to reimburse Boeing for their share of payments Boeing made on their behalf to third-party creditors. Energia and Yuzhnoye countered that they had unwritten assurances from Boeing that they would not seek such repayments.

In September, the court issued a summary judgment in favor of Boeing. Energia owes Boeing at least $298 million, according to the filing, but has not paid any of that amount to date. A trial involving two of Energia’s subsidiaries is complete and a judgment is pending.

While a U.S. court’s ability to block the sale of a company controlled by the Russian government would appear limited, Boeing’s leverage is in the form of Sea Launch’s two biggest assets: its mobile launch platform and assembly and command ship (ACS). Both those ships, used by Sea Launch to carry out its launches, are located at the Port of Long Beach, California, which served as its home port since the 1990s.

“To the best of Plaintiffs’ knowledge, the Platform and the ACS are the only significant assets that Energia owns and controls in California,” the Boeing filing stated. “If these assets are sold and the proceeds removed from the Court’s jurisdiction before this case is concluded and Boeing is paid, Energia would — yet again — delay Boeing’s collection efforts and circumvent paying Boeing a debt it plainly owes.”

Boeing requested that, if the sale of Sea Launch does go forward, the court should direct that the proceeds go into a U.S.-based escrow account so that they can be used to pay Boeing’s judgment.

A hearing on the motion for a preliminary injunction is scheduled for May 2 in Los Angeles.