WASHINGTON ― U.S. antitrust regulators have extended their probe into Lockheed Martin’s proposed $4.4 billion purchase of rocket manufacturer Aerojet Rocketdyne so that the two companies can provide more information to the government, the companies announced Friday.

The customary 60-day antitrust review process for the deal, announced in December, was supposed to end at midnight Thursday, but it will last 30 days longer, the companies said.

“We are working cooperatively with the Federal Trade Commission as it conducts its review of the transaction and we continue to expect to complete the acquisition in the second half of 2021,” Lockheed said in a statement.

Reuters reported Wednesday that regulators would likely extend the review period.

The announcement comes after Raytheon Technologies CEO Greg Hayes said Wednesday it would challenge the deal with regulators. The concern is that Lockheed, a top competitor, would absorb a key supplier of its solid-fuel rocket motors, stifling completion in the missile market.

Lockheed Chief Financial Officer Ken Possenriede has said the combined company would continue as a merchant supplier across the industry and be able to cut costs for the government and civil space market.

Northrop Grumman bought rocket maker Orbital ATK in 2018 under similar terms, but Boeing argued when it dropped out of the Air Force’s competition to build new intercontinental ballistic missiles, Northrop’s acquisition had given it an advantage.

The “second” review process is a massive, expensive undertaking in which the government typically seeks information from the companies and industry experts, said mergers and acquisition attorney Kenneth Lefkowitz, of Hughes Hubbard & Reed. From there, the government will typically negotiate with the parties on the terms of the deal.

Lefkowitz speculated that because regulators with the incoming Biden administration have been swamped, it could take nine months for the Federal Trade Commission to formally act on the deal.

That tracks with Lockheed’s projection that the deal could take until the second half of the year to close.