The Justice Department sued French aerospace company Safran SA to block its $1.8 billion acquisition of an actuation and flight control business from RTX Corp. but offered to let the deal through if Safran divests certain assets to resolve antitrust concerns.

Safran’s proposed acquisition of the RTX business, first announced in 2023, would substantially lessen competition in violation of Section 7 of the Clayton Act if no changes are made, the DOJ said in a complaint Tuesday in the US District Court for the District of Columbia. RTX, formerly known as Raytheon, is also a named defendant.

Safran and Arlington, ...