NEW YORK (CNN/Money) - United Airlines filed for protection under Chapter 11 of the U.S. bankruptcy laws Monday in the largest bankruptcy in the history of the airline industry, according to wire service reports.

United, the world's second-largest airline, was widely expected to file for bankruptcy after a federal board refused to grant it $1.8 billion in loan guarantees. Sunday night, the carrier, a unit of UAL Corp., completed its application for $1.5 billion in financing that would allow it to continue to operate while bankrupt.