Just when BP (NYSE: BP) looked like its recovery from the Deepwater Horizon disaster was starting to strengthen, here comes news that the U.S. government is suing.

BP, along with eight other companies including rig owner Transocean (NYSE: RIG), will face allegations under the U.S. Clean Water Act and Oil Pollution Act that they violated environmental laws, failed to keep the well under control, failed to appropriately monitor the well's condition and safety, and failed to provide adequate safety for employees and for the environment.

Unlimited liabilities
If the suit is successful, the companies involved could end up being stuck with unlimited liabilities for all cleanup and damages costs. Some commentators are suggesting that could add more than $20 billion to the $30 billion that BP has already coughed up for the cleanup operation.

The actual sum will depend on the amount of oil spilled, with the Clean Water Act allowing for penalties of $1,100 per barrel (or in some specific circumstances, up to $4,300). Estimates of the total amount spilled, in the aftermath of the explosion which also killed 11 workers, vary widely.

The news doesn't come entirely out of the blue, since there has been a possibility of a lawsuit for some time, but the U.S. attorney general did, in ominous-sounding terms, say that this is just the first step in holding BP accountable for the spill. He also said that a criminal investigation is continuing in order to identify those responsible.

Government commission
The government-appointed commission investigating the incident named BP, Transocean, and Halliburton (NYSE: HAL) as three companies whose decisions around the time of the disaster were questionable. Of the three, the U.S. contractor Halliburton is notable by its omission from the current lawsuit.

Perhaps surprisingly, this latest threat only knocked a few pennies off BP shares, and they currently stand quite a long way back from where they plumbed in the immediate aftermath of the disaster.

But then, this is an enormously complex case that is likely to take a very long time to reach a verdict, and to cost a lot of money along the way. Most parties will probably be expecting some sort of settlement to be agreed rather than fighting to the bitter end.

Is it fair?
What do you think? Is this action justified and fair, and is it a price that BP will just have to pay and look as cheerful as possible about? Or is it a bit of saber-rattling by the Obama administration looking for a second term of office?

Share your thoughts below.

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This article has been adapted from our sister site across the pond, Fool U.K.

Alan Oscroft owns BP shares. The Fool owns shares of Transocean. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.