Rocket builder United Launch Alliance, the joint venture of Boeing and Lockheed Martin, will require all employees to receive vaccinations against Covid-19 beginning Sept. 1, CNBC has learned.

“The recent increase in cases in our communities and among our teammates is beginning to stress the schedule and negatively impact our ability to meet our commitments to our customers,” ULA CEO Tory Bruno wrote on Wednesday in a company-wide email obtained by CNBC. “We have heard your concerns and do not take this step lightly.”

A ULA spokesperson confirmed the requirement in a statement to CNBC that matched Bruno’s announcement.

The company – headquartered in Centennial, Colorado, with operations in Alabama, Texas, Florida, and California – is one of the top manufacturers of large rockets, and the main U.S. competitor to the rocket business of Elon Musk’s SpaceX in winning government contracts for launches. ULA has launched two missions so far this year, and was set to launch Boeing’s Starliner test flight earlier this month as its third before the spacecraft was delayed due to propulsion valve issues.

ULA’s announcement makes it one of the first publicly-confirmed space companies to require Covid vaccines.

Bruno noted that ULA employees who have not yet received the full Covid vaccine will be required to receive a first dose by Sept. 30 and the last dose by Oct. 31. He also noted that ULA’s requirement “is subject to bargaining with our unions,” which the company will meet with to reach bargaining agreements.

“This requirement is in alignment with our U.S. government customer and industry direction and will place us in a much better position to meet the nation’s needs and our [launch] manifest commitments while protecting the health of everyone at our facilities,” Bruno added in the email.