Viola will replace Brian Matusz on the 25-man roster.
This is a short-term move. Viola will give the Orioles an extra southpaw in the bullpen to counter the Braves' left-handed hitters, but he's not expected to stay long.
Viola made one appearance with the Orioles this season, retiring all five Seattle Mariners that he faced. He joined the club in Washington, but wasn't recalled. He's used to riding that shuttle to Bowie.
Viola is 3-1 with a 2.25 ERA in 24 appearances with the Baysox. He recently was chosen to the Eastern League All-Star team.
Also, left-hander Clay Rapada has cleared waivers after being designated for assignment earlier this week.
That's the next step, but not the last one.
Rapada can refuse the assignment to Triple-A Norfolk because he's been outrighted previously, but he's expected to accept it. The Orioles have discussed the situation with his agent.
Rapada was designated on Wednesday to make room for Alfredo Simon on the 25-man roster. Left-handers were 4-for-35 against him, with one home run, three walks and 13 strikeouts. However, right-handers were 9-for-13 with two doubles, one triple, two home runs, three walks and no strikeouts.
The Orioles didn't believe they could carry a left-handed specialist who might need to be replaced after one or two batters. Their starters aren't pitching deep enough into games for that luxury.