Jack Raisner, an attorney for the plaintiffs, told Reuters that the termination is a "harbinger" of likely bankruptcy.

Raisner, who represented employees of Solyndra, the government-backed solar panel maker that terminated its employees shortly before filing for bankruptcy in 2011, said Fisker's current situation is similar to Solyndra's final days.

"It feels like almost deja vu," he said.

The Energy Department's loan program has been under scrutiny ever since Solyndra's bankruptcy. Since then, other US-backed companies have gone bankrupt, notably Fisker's battery supplier formerly known as A123 Systems and now called B456 Systems Inc.

April 22 payment looms

Fisker, which was founded in 2007, hopes to renegotiate a DOE loan payment due on April 22, which the source familiar with Fisker's finances said was around $10 million.

In 2009, the DOE awarded Fisker a $529 million loan as part of a US program to finance advanced vehicle development. Fisker pledged its assets, including equipment and property, as collateral on the DOE loan, according to the loan agreement dated Sept 18, 2009.

The company's flagship vehicle, the $100,000-plus Karma plug-in hybrid, quickly won accolades for its styling and cachet with celebrities, including pop star Justin Bieber and actor Leonardo DiCaprio, who is also an investor in the company.

Fisker used $193 million of the DOE loan and earmarked the rest for a second plug-in hybrid, the Atlantic, but the DOE froze the credit line after delays in launching the Karma. The last payment from the DOE came in May 2011.

"The Department of Energy stopped payment on the federal loan in 2011 after Fisker stopped meeting their milestones, and is committed to the best outcome for taxpayers," DOE spokeswoman Aoife McCarthy said in a statement.

"Despite Fisker's difficulties, our overall loan portfolio of more than 30 projects continues to perform very well, and more than 90 percent of the $10 billion loan loss reserve that Congress set aside for these programs remains intact," she said.

Fisker has not produced a car since July and has been seeking a financial backer to help finish the development of the Atlantic and produce it at a Delaware plant.

Chinese automakers Dongfeng Motor Group Co Ltd and Zhejiang Geely Holding Group both considered buying a majority stake in Fisker, but they balked at the terms of Fisker's loan agreement with the DOE.