United Airlines CEO Scott Kirby has floated a possible combination with American Airlines, Bloomberg reported on Monday, citing people familiar with discussions on the matter. 

Shares in American Airlines jumped more than 4% in early premarket trading Tuesday, while United Airlines climbed about 2%. 

Kirby pitched the idea to senior government officials, Bloomberg reported, and it remained unclear if there were any processes for an actual deal. Reuters also reported a similar development.

United Airlines (NASDAQ:UAL) and American Air (NASDAQ:AAL) are the second and fourth-largest U.S. airlines by market capitalization, with any potential merger standing to create the country’s biggest carrier, above Delta Airlines. The two also have the largest fleets among U.S. airlines with more than 1,000 aircraft each. 

The Bloomberg report noted that such a merger would likely face intense scrutiny over its competition effects, even under the business-friendly Trump administration. 

A potential merger also stands to further consolidate the U.S. domestic carrier market, which is controlled by American, Delta, United, and Southwest.