Fitch Ratings on Monday downgraded the credit ratings of Telephone & Data Systems Inc. and its subsidiary United States Cellular Corp., the country's sixth-largest wireless carrier by number of subscribers.

Fitch downgraded both companies from "BBB+" to "BBB," the lowest "investment-grade" rating, saying there's increasing pressure on them, particularly in wireless. Competition and a weak economy with high unemployment play a part, the ratings agency said.

US Cellular recently cut its forecast for earnings before interest, taxes, depreciation and amortization, Fitch noted.

On the positive side, TDS has a "solid" financial profile with good liquidity and a conservative balance sheet, Fitch said.

TDS shares fell 43 cents, or 1.4 percent, to $30.81. U.S. Cellular shares fell 20 cents, or 0.5 percent, to $43.48.