Leading Brazilian fixed-line telecom Oi (OIBR)   has just achieved a new No. 1 after filing for Brazil's largest bankruptcy protection in the country's history.

The company, which has since February been reviewing its option to raise funds and cut debt, sought protection after it was unable to agree with major shareholders on a plan to reorganize its 65.4 billion reais ($19.2 billion) of debt.

Oi said in a securities filing that "obstacles confronted by management to finding a viable alternative with creditors" prompted it to seek protection from creditors. The company will continue to operate as normal during this period.

The move marks a sharp turnaround from the company's outlook in April, when the Rio de Janiero provider of telecoms services entered into a nondisclosure agreement with Moelis, the financial adviser to a group of its bond holders. At the time it noted it was "an initial step toward productive and expeditious discussions regarding the terms of a potential restructuring."

Oi had been exploring its financial and strategic alternatives to optimize its liquidity and debt profile a $4 billion investment from Russian billionaire Mikhail Fridman collapsed in February.

Oi's efforts to reverse its fortunes have been made more difficult by political and economic upheaval in South America's largest country. Brazil remains mired in one of the worst recessions it's seen in a generation, with GDP forecast to contract by up to almost 3.9% this year. That's been compounded by a political crisis which has led to the impeachment of President Dilma Rousseff.

Oi said on May 12 that first-quarter revenue fell 4.4% to R6.5 billion. Ebitda dropped 12.6% to R1.68 billion. Capital expenditure increased 22.3% amid a company push to modernize its network.