CHICAGO (CBS) -- Chicago's aldermen have for decades wielded power of licensing, permitting and zoning in their wards, but is that power being abused?
It is often referred to as aldermanic prerogative.
One former building owner says he caught one alderman abusing that power, and it is all on camera.
CBS 2 Investigator Dave Savini has been digging into the case for two years.
"He threatened to send inspectors," said Brian Strauss, the former owner of the building that once housed the iconic Double Door Concert Hall.
He says no one understands the power of aldermanic prerogative more than him, and he learned the hard way the day his alderman showed up at his property and vowed to take away his zoning status.
Joe Moreno is the man in cell phone video talking to Strauss in 2017.
"You're in my space," Strauss can be heard saying.
"Nothing is going to happen in this building," Moreno says in the video. "It's going to be an empty building for you or your family."
"He was trying to bully me basically," Strauss says now.
Moreno was recently voted out of office, but not before turning Strauss' once lucrative property rental business into a financial nightmare.
"I'm going to have inspectors here on a daily basis. You watch," Moreno said on the video. "And I don't think you're a man..."
Strauss says Moreno surprised him at his front door on the day the tenants who operated the concert hall were being ordered to move out. The tenants were Moreno's campaign contributors, and Strauss had them evicted.
"Please don't threaten me," Strauss says in the video.
"I'm not threatening you," Moreno responds. "It's a promise. There's a difference. A threat means it's not going to happen."
Moreno can be heard telling Strauss he's going to use his power to make sure Strauss would never maintain his zoning to rent or sell his property to anyone else.
Moreno can be heard threatening to downzone the Wicker Park property that Strauss' family owned since 1977.
"And by the way, when the leases are up there, since there is downzoning, you can't sign new leases for your tenants. So whenever those leases are up and those guys want to leave, and you want to sign a new lease with a new tenant, you're not going to be able to. I'm being up front with you," Moreno says.
"He abused his power to get even with this man and his family because they evicted his pals," Strauss's attorney James McKay Jr. said.
Soon after the video Moreno made good on his promise, but Strauss says, he was never given a reason why he was downzoned.
"It was just because of pure revenge," he said.
The city council backed Moreno when the vote for downsizing was called.
"They didn't care because they have their zoning matters in their own ward," McKay said. "It's give and take. The aldermen will scratch each other's back. That's how aldermanic prerogative or aldermanic privilege works."
Changing a zoning status is one of the powers referred to as aldermanic prerogative.
As Moreno was getting voted out of his First Ward aldermanic office, Lori Lightfoot was getting voted in as mayor.
She promised to end aldermanic prerogative.
"These practices have gone on for far too long," she said as she promised to end aldermanic prerogative. "This practice breeds corruption. Stopping it isn't just in the city's interest. It's in the city council's interest."
She then turned to stare down the 50 newly sworn in aldermen.
Of course, Moreno wasn't there.
"I am proud to say that he is no longer an alderman," Strauss said.
The Double Door space stayed empty for a year and a half, and now Strauss is taking Moreno and the city to court for the money he lost.
Strauss says he lost "well over several million dollars."
Strauss and his attorney also want Moreno investigated for what they say happened during a 10th floor city hall meeting with Moreno and other city officials.
"He was actually trying to orchestrate the sale of the building," Strauss said.
Strauss claims in the meeting Moreno gave him another chance to avoid the downzoning and told him he could if he sold the building for $3 million less than it was worth.
He says it all happened right in front of another alderman who was the head of the zoning committee -- Danny Solis, former alderman turned FBI mole.
"He consistently rolled his eyes. It was very obvious that he knew what was happening was very wrong," Strauss said.
Strauss said he hopes Solis was wearing a wire that day.
If he had a wire on that day, the feds would hear "Moreno telling me right to my face with a lot of derogatory foul language words that you will never have an effing tenant in this building," Strauss said.
"It was absurd. I hope Solis was wearing a wire. I really do. Oh man, that would be great, great television," McKay said.
Strauss's attorney says Solis will be called for a deposition if a judge rules to let the case go forward, and the cell phone video will also be entered as evidence.
Moreno has repeatedly said he did nothing wrong.
The city law department declined to comment on the case.
Strauss did eventually sell his building buts says the delays cost him millions.
After the sale, the new owners got the better zoning reinstated.
Strauss's suit against the city goes before a judge next week.
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