The firm also lowered its price target for the shares to $3 from $5.
Alpha Natural Resources is down 2.0% to $4.78 in pre-market trading Wednesday.
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The downgrade follows analysts concerns of a bleak forecast for the met coal sector.
"Our Sell rating is valuation driven, given the sharp downgrade to met coal forecasts by our Commodity Team. While Alpha's eastern thermal realizations are expected to approach $70/ton by 2016-17 based on a $5/mmBtu gas price, our EBITDA forecast in 2015 is 53% below the Street," UBS said.
"The cut to our met coal price deck reflects a larger oversupply view despite our model assuming 9 metric tons of US production cuts this year. In addition, the latest benchmark settlement of $120 per metric ton was lower than expected and down 16% from $143 per metric ton in the first quarter," analysts reported.
Separately, TheStreet Ratings team rates ALPHA NATURAL RESOURCES INC as a Sell with a ratings score of D. TheStreet Ratings Team has this to say about their recommendation:
"We rate ALPHA NATURAL RESOURCES INC (ANR) a SELL. This is driven by several weaknesses, which we believe should have a greater impact than any strengths, and could make it more difficult for investors to achieve positive results compared to most of the stocks we cover. The company's weaknesses can be seen in multiple areas, such as its unimpressive growth in net income, poor profit margins, weak operating cash flow and generally disappointing historical performance in the stock itself."