The bipartisan legislative ethics commission voted unanimously to release the report, which is expected to detail Welch's response to allegations against former Illinois state Rep. Harry Benton. Benton resigned earlier this year under pressure from Welch after complaints were brought to the speaker's attention in February.
Political observers say the report could test Welch's leadership at a moment when additional concerns have surfaced.
ABC7 political analyst Laura Washington said, "I think Chris Welsh is in significant trouble. I think this first crisis, a major crisis of his leadership, and I think he's going to have a lot of work to do to hold on to his power."
Welch is also facing scrutiny over how he responded to similar complaints raised by a Benton staffer three years earlier, as reported by the Chicago Tribune.
House Republican Leader Tony McCombie criticized Welch's handling of the earlier allegations, saying, "Not only not speaking to him about it, not reprimanding him then, he didn't remove him from the caucus then. Then he continues to spend one point four million dollars to get him re-elected. That's a real problem."
Republicans have also launched a political ad highlighting Welch's use of his professional Instagram account to like posts featuring women in swimsuits. Washington said the issue could resonate among Democratic women in the legislature.
"Particularly, there's going to be major concerns coming from the women's caucus, as you know. Mike Madigan fell from power largely because of their concerns and their influence, and so I think that same group is going to be asking some very tough questions of Chris Welch later this week," Washington said.
Some Democrats are urging patience until the report is released.
"I just want to gather all the facts," said Illinois state Rep. Marcus Evans of Chicago. "Do I think? I mean, I support him for Speaker, I support, I think he's a great person. I think his record speaks for himself. He's done a great job."
Welch's communication director said the speaker was not available for an interview Monday. The station requested comment on the political ad but had not received a response as of publication time. The Legislative Ethics Commission is expected to release the Benton Report on Friday.