WASHINGTON (AP) -- A Democratic senator is calling for federal investigations into possible price gouging of natural gas in the Midwest and other regions following severe winter storms that plunged Texas and other states into a deep freeze that caused power outages in millions of homes and businesses.

Minnesota Sen. Tina Smith says natural gas spot prices spiked as high as 100 times typical levels, forcing utilities and other natural gas users to incur exorbitant costs, many of which were passed on to customers.

In a letter sent Saturday to federal regulators, Smith said price spikes could "threaten the financial stability of some utilities" that lack sufficient cash reserves.

A copy of the letter was obtained by The Associated Press.

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