United Airlines (UAL) and American Airlines (AAL) are facing scrutiny from a group of US senators over a potential merger that lawmakers warned could raise airfares and reduce flight options for travelers, The Wall Street Journal reported Monday, citing a letter.

In a letter to United Chief Executive Scott Kirby and American Airlines Chief Executive Robert Isom, the senators, including Elizabeth Warren and Mike Lee, said a combined airline could "exploit market power" in overlapping routes and harm consumers, according to the report.

The lawmakers asked both carriers to disclose by May 3 details of any merger-related discussions and analyses of a potential deal's impact on fares, routes and employees, the report said.

American Airlines on Friday said that it is "not engaged with or interested in any discussions regarding a merger" with United Airlines.

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