Lohse appealed the penalty, and can continue to play until a hearing is held. Asked about the suspension, he called the ruling "pretty weak."
St. Louis manager Tony La Russa said he had not been expecting a suspension.
"The other guy threw two balls at guys' heads," La Russa said. "I don't know, I'm just shocked."
Major League Baseball disciplinarian Bob Watson also fined Lohse an undisclosed amount.
St. Louis is second in the NL wild card race. The Cardinals played Pittsburgh at home on Wednesday night.
Trouble between Lohse and Volquez started in the fifth inning of the Reds' 7-3 win Sunday at Cincinnati.
Lohse batted in the top half with two runners on base, and Volquez threw up-and-in to the Cardinals pitcher. Volquez led the bottom half and Lohse's first pitch was high-and-tight, leading plate umpire Greg Gibson to warn both teams.
"Same spot," Lohse said after the game. "Wasn't trying to hit him, though."
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