Madigan claimed no wrongdoing on his part or from anyone within his office.
The Senate Women's Caucus stood behind Cassidy and called on Legislative Inspector General Julie Porter to investigate. Soon after the group called for the investigation, Speaker Madigan did the same and said his office would cooperate.
State Sen. Melinda Bush, a Grayslake Democrat, said Madigan's prompt response was the right thing to do.
"If our asking pushed the Speaker to do that, then we will take that as a victory. It's so important that we change the culture of this place."
She said the speaker's cooperation with the investigation shows he takes them seriously. "We just want to make sure women feel safe, that they aren't intimated or harassed and when they are --or when they feel they have been that it's dealt with swiftly and timely."
Cassidy and many other lawmakers have been vocal about harassment during the #metoo movement, sharing their own stories. Several task forces were created in response to reports of sexual harassment from lobbyists and staffers in the statehouse.