Robert Redford and Paul Newman would be proud.

New York City Assemblymember Linda Rosenthal went undercover at several Airbnb listings in the city to expose what she says is a "pervasive" illegal hotel problem. Recordings from the sting reveal hosts knowingly breaking the law, even going so far as to instruct the undercover guests not to mention Airbnb in the building.

See also: New York Goes to War Against Airbnb for Disrupting Hotel Business

“If somebody asks you something, never mention in the building Airbnb,” a host tells Rosenthal."This is supposed to be residential."

The assemblymember rented out four apartments for one night each during the week of April 13 to 20. When Rosenthal went to check in, she brought along a hidden camera, as one does in the true network-television sting tradition.

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"I think it's an excellent way to actually show the problem," Rosenthal told Mashable on Friday. "It's a useful way to crystalize the situation."

The assemblymember is not new to going undercover: In 2007, before Airbnb was a major player in the market, she also investigated illegal rental listings, and has gone undercover to expose the mislabeling of fur in department stores.

As stings go, the investigation in April was quite successful.

Rosenthal, working with journalists at CBS New York, found management companies posing as tenants, landlords converting residential buildings into hotel-style lodging, and one rental company with over 200 listings. New York City housing law prohibits rentals of residential units for less than 30 days.

Share Better, a coalition of elected officials and community activists created to "fight illegal hotels," financed the sting.

Airbnb has repeatedly said that illegal hotels do not accurately represent the listings on its website. However, the company has also repeatedly declined to publicly release data about its listings. That's left proponents of home sharing and elected officials at an impasse, as Airbnb says laws should allow locals to occasionally rent out their own homes, while officials say they do not have enough information about who is breaking the law.

Instead of making progress on the issue, it seems the two sides are talking past each other.

"Nobody supports bad actors who turn apartments into large-scale illegal hotels," Airbnb spokesperson Nick Papas told Mashable in a statement. "We have removed thousands of listings from our site and Ideal Oasis is prohibited from accepting reservations on our site."

Ideal Oasis was the large-scale operation exposed in the undercover video.

Papas said hosts must confirm that they will follow the rules, and that Airbnb provides "substantial information" to hosts before they list on the site.

"We agree with New York City leaders that enforcement agencies should be targeting illegal hotel operators, many of whom do business on multiple websites," he added. "At the same time, we need to clarify the laws, so regular New Yorkers can share the home in which they live and pay the bills."

Rosenthal, however, says the law is crystal clear. "They want it to be changed to enable this kind of rental to continue," she said.

Rosenthal added that the responsibility to stop the use of rental units as short-term lodging for tourists is on both New York City and companies, like Airbnb, which make it easy for bad actors to list residential units.

The company has changed how it notifies hosts about local laws. Currently, on Airbnb's website, a popup appears when an address within the city limits is listed.

The popup warning on Airbnb's website that appears when listing an apartment in Manhattan. Image: Airbnb

The New York State Multiple Dwelling Law (available here) prohibits short-term rentals of property in Class A multiple dwellings used for permanent residence purposes (which includes most apartment buildings but not single and two-family buildings) unless a permanent occupant of the apartment is present during the stay, no money is exchanged, or if the stay is longer than thirty consecutive days.

However, Rosenthal does not think Airbnb's current warnings go far enough.

"If they were really trying to be careful," she said, "they would put in big bold letters on the first page 'Here is where this activity is illegal.'"

The assemblymember added that New York City should move to do more to enforce the laws, which are presently based on complaints. A few more complaints have come in, though, since her undercover video aired Thursday on CBS New York.

"Since that aired, I'm getting emails and calls from tenants saying 'Oh, I've seen this happening in my building,'" Rosenthal said, adding that she'll be forwarding those complaints to the office that enforces the illegal hotels law.