Regulator RAE called the emergency meeting on 1 June after receiving a letter from Greece's natural gas company DEPA, dated 31 May, threatening to cut supplies to electricity producers if they failed to settle their arrears with the company.
An energy crisis would add to the debt-stricken country's political and financial strains, threatening households and businesses with power cuts ahead of a 17 June election which may decide if the country will stay within the euro (see background).
The Greek government already risks running out of cash next month if it fails to receive fresh bailout funds from its lenders.
"RAE is taking crisis initiatives throughout next week to avert the collapse of the natural gas and electricity system," the regulator's chief, Nikos Vasilakos, told Reuters.
RAE has summoned DEPA and the affected companies to a meeting on 6 June, Vasilakos said.
According to an energy industry source who declined to be named, DEPA has no cash to settle gas supply bills worth a total €120 million with Italian gas firm Eni , Turkey's Botas and Russia's Gazprom, which fall due this month.
DEPA CEO Haris Sachinis declined to comment on the company's cash position but told Reuters: "DEPA is taking every action to avoid owing anything to its suppliers."
If DEPA cuts off supplies, Greece's independent power producers such as Elpedison, Mytilineos, Heron and Corinth Power - which cover about 30% of the country's power demand - would be forced to stop operations.
Greece's grid operator ADMIE would then have to proceed to rotating power cuts to avoid a general blackout, just as the country's summer tourism season, a rare foreign exchange earner for the country's uncompetitive economy, goes into full swing.
These producers use natural gas, much of it supplied by DEPA, to produce about 70% of their electricity output. Greece's dominant electricity company PPC uses natural gas to a much lesser extent than the other producers, but PPC's coal and hydro units would not be able to cover the shortfall.
Power companies have failed to pay their bills to DEPA because they, in turn, have not been reimbursed by LAGHE, a state-run clearing account for the nation's energy transactions.
In recent months RAE has repeatedly urged the government to shore up the accounts of LAGHE, which is sitting on a deficit of more than €300 million.
The account went into deficit because its receipts have not matched the generous subsidies it pays out to renewable energy producers, particularly for solar panels.
LAGHE's deficit deteriorated earlier this year when two electricity retailers, PPC's biggest rivals, went bust without honoring their obligations to the account, leaving authorities scrambling to find cash.
The easiest way to do this would be to take out a loan of between €300 and €400 million from the state-run Loans and Consignment Fund, which has the cash sitting in a so-called "Green Fund" for environmental purposes.
But the so-called "troika" of Greece's international lenders, the European Union and the International Monetary Fund (IMF), refuse to approve this move, PPC Chief Executive Arthouros Zervos told Reuters in an interview.
EU Commission ‘too dogmatic’
Zervos said the troika, particularly the European Commission, was worried that the liquidity injection would constitute illegal state aid and remove incentives to fix Greece's flawed energy system.
"They are seeing things too dogmatically," Zervos said.
Greece could also boost the LAGHE account by using about 100 million euros sitting in the accounts of the two power retailers that went bust earlier this year, Zervos said.
But energy authorities have no access to that money because it has been frozen as part of a criminal investigation into the bust. "It's absolutely crazy. This is money that power consumers paid into the energy system," the source said.
Greece's political limbo doesn't make things easier. Under Greek law, caretaker governments have a limited mandate and are loath to take major initiatives without approval from party leaders.