The Before He Cheats hitmaker, who is married to ice hockey player Mike Fisher, took to her Instagram.com account on America's Labor Day holiday on Monday to announce the exciting news to her followers.
Underwood posted a photo of herself with her two dogs, sporting shirts revealing they are going to become a "big brother" and "big sister", and in the accompanying caption, she wrote, "In honor of 'Labor' Day, Ace & Penny would like to make an announcement. Their parents couldn't be happier..."
Underwood married her NFL player husband in 2010.
The 31-year-old singer became famous after winning "American Idol." She can now call six Grammys her own and she has sold more than 15 million albums worldwide.