Struggling regional airline Mesa Air said on Wednesday its shareholders approved a plan to issue as many shares as necessary to buy back all the company's senior convertible bonds, due in 2023.

Mesa Air -- which runs regional services for United Airlines, US Airways and Delta Air Lines -- aims to shore up its finances as the industry is hit by high fuel costs and weakening demand.

Six airlines have filed for bankruptcy in the past five months. Mesa's shares have dropped nearly 80 percent this year, closing at 64 cents on Nasdaq on Wednesday.

The company, which said earlier on Wednesday it would close operations of its Air Midwest unit, is fighting a plan by Delta to terminate a contract with Mesa's Freedom Airlines unit to provide regional services.

Mesa, which also schedules flights under its own name and runs a low-cost service under the name go! in Hawaii, fired its chief financial officer last year after a US judge ruled Mesa had to pay Hawaiian Airlines hefty damages in an unfair competition case.

Mesa has been identified by industry analysts as a possible bankruptcy candidate, as conditions worsen in the air travel business. The company's general counsel, Brian Gillman, declined to comment on Wednesday on the likelihood of a bankruptcy filing.

Since late December, six airlines have declared bankruptcy, with only one, Frontier Airlines, still flying. Eos Airlines, Skybus Airlines, ATA Airlines, Aloha Airlines and MAXjet Airways have all stopped flying or are in the process of winding down operations.