Under Armour shares closed 2.4 percent lower on Friday after U.S. Speedskating sought permission to switch to different Under Armour suits, The Wall Street Journal reported.
Friday evening, the team announced its athletes would return to the skin suits they used at the recent World Cup competition for the rest of the Sochi games. Those suits are also made by Under Armour.
Some skaters believed the high-tech racing suits were causing the team to underperform at the Olympics.
(Read more: US struggling at oval, focus on high-tech suits)
"Vents on back of the suit, designed to allow heat to escape, are also allowing air to enter and create drag that keeps skaters from staying in the low position they need to achieve maximum speed," sources with knowledge of the matter told the Journal.