The U.S. Department of Transportation has fined Denver-based Frontier Airlines and two other airlines for violations of consumer protection rules.

Denver-based Frontier -- the No. 3 airline at Denver International Airport -- was hit with the biggest fine, $400,000, "for violating the department’s oversales and disability rules," the U.S. DOT announced Friday.

"The department found that Frontier failed to seek volunteers before bumping passengers involuntarily, failed to provide bumped passengers the required written notice describing their rights, and failed to provide proper compensation to passengers in a timely manner, in violation of DOT rules," the agency said.

"In addition, Frontier failed to provide passengers with a disability prompt and adequate wheelchair assistance in enplaning and deplaning aircraft and moving within the terminal, and did not adequately respond to complaints filed by passengers with disabilities," it said.

Read more at the Denver Business Journal: http://bit.ly/2v0pUvE