Shares of Health Management Associates Inc. plunged in premarket trading Tuesday after fellow hospital operator Community Health Systems announced plans to buy the company at a discount to its current stock price.

Shares of Health Management Associates Inc. plunged in premarket trading Tuesday after fellow hospital operator Community Health Systems announced plans to buy the company at a discount to its current stock price.

Health Management Associates, or HMA, also said it expects second-quarter earnings to fall well below Wall Street expectations, and said it received a fresh round of subpoenas from federal regulators.

Community Health Systems said it will pay a combination of cash and stock valued at $13.78 for each HMA share.

That represents a drop of more than 7 percent from HMA's Monday closing price Monday of $14.92. HMA shares had climbed more than 60 percent, as of Monday, since they closed 2012 at $9.32.

But the stock sank more than 5 percent, or 78 cents, to $14.14, in premarket trading Tuesday. Community Health shares, in contrast, rose about 2 percent, or 89 cents, to $48.12.

Community Health said its deal totals $3.9 billion, or $7.6 billion counting assumed debt. The board members of both companies have approved the deal, but HMA stockholders and regulators still have to clear it.

Separately, HMA said it expected to report earnings of between 10 cents and 11 cents per share in the second quarter on revenue of about $1.46 billion. The company said its revenue from established hospitals is expected to fall due in part to a shift in the payer mix, a reduction in surgeries and rising bad debt.

Analysts expect, on average, earnings of 20 cents per share on $1.72 billion in revenue, according to FactSet.

"It's a really poor performance, and if ever there was a reason for change in control, this was it," said Sheryl Skolnick, an analyst who follows the company for CRT Capital Group.

HMA also said it has received more subpoenas from the U.S. Department of Health and Human Services and the Office of the Inspector General that supplement subpoenas it received in 2011 regarding emergency room operations.

The company also received another subpoena that supplements one received about two years ago regarding physician relationships.