Another company is learning about the fine points of Section 333 of the Communications Act, which prohibits willful interference with any licensed or authorized radio communications. This time, it’s the folks who provided the Baltimore Convention Center’s in-house WiFi service who were caught by the FCC trying to block individual WiFi hotspot users from going online. Meanwhile, Hilton is also being slapped with a proposed fine for its failure to comply with an investigation into its alleged hotspot blocking.

Virginia-based M.C. Dean is a huge contractor for electrical and communications systems, and provides telecom services, including WiFi to the Baltimore Convention Center (BCC), where exhibitors were charged several hundred dollars if they wanted access to the BCC WiFi network.

But some exhibitors get better wireless data pricing through — or have needs that are better met by — the use of WiFi hotspots that connect to cellular data networks.

According to a newly released FCC notice of apparent liability [PDF] the commission received a complaint on Oct. 23, 2014, from a company that offers competing WiFi service, alleging that M.C. Dean’s system was sending out “deauthentication frames” to inhibit hotspot users from maintaining a connection between their hotspots and their other devices, thus preventing them from working properly.

The complainant alleged that M.C. Dean’s actions were identical to those that had earned Marriott a $600,000 fine only weeks earlier.

FCC investigators visited BCC three times in the weeks that followed, first confirming that their independent WiFi hotspots worked outside the convention, but not inside, then confirming M.C. Dean’s use of deauthentication frames to cause these disconnects.

When confronted by inspectors, an M.C. Dean staffer acknowledged the blocking but said that visitors still had access to the BCC’s free WiFi network. But the FCC notes that this access was only available in the public lobbies of the BCC and not on the exhibitor floor, where M.C. Dean charged anywhere from $795 to $1,095 for access.

The company later confirmed that it had, since Oct. 2012, been using deauthentication tech to block non-M.C. Dean WiFi access at the convention center.

While one might shrug off the company’s crass attempt to cash in from convention attendees, the FCC notes that there is evidence that M.C. Dean’s auto-blocking system reached beyond the walls of the BCC, meaning the company was screwing over people — and web-connected buses, cars, and trains — who had nothing to do with the conventions.

M.C. Dean tried to defend the illegal hotspot blocking by saying its intended purpose wasn’t to gouge exhibitors or drive out competition, but to “detect and prevent malicious attacks on the wireless network and improve network security and reliability.” However, the FCC says the company provided no evidence of how blocking WiFi hotspots was going to achieve that desired end.

The company also argued that it didn’t do anything horrible because it had whitelisted a handful of pieces of equipment from the auto-blocking system, but the FCC this is just more proof that the company was deliberately blocking the rest of the users.

Then there’s M.C. Dean’s claim that all was okay because it left unblocked a total of two of the dozens of available WiFi channels. This argument did not win over the FCC, which writes that “M.C. Dean offers no evidence that any device that was blocked by M.C. Dean would be capable of automatically finding the one channel in each band that was left unblocked. Such automatic capability does not appear to be standard among Wi-Fi devices and, if it were, it would still force all such devices to share a single channel that could become highly congested and perhaps unusable.”

Finally, M.C. Dean tried to make the case that its blocking of third-party hotspots constituted allowable “network management,” and was not malicious. Again, the FCC disagreed, saying that the company “sought to cause, and in fact did cause, harmful interference to lawfully operated third-party networks… M.C. Dean knew that its system would cause interference to other Wi-Fi devices – in fact, that was the company’s goal.”

The FCC is now proposing a fine of $718,000 against M.C. Dean.

“Consumers are tired of being taken advantage of by hotels and convention centers that block their personal Wi-Fi connections,” said Travis LeBlanc, Chief of the FCC’s Enforcement Bureau. “This disturbing practice must come to an end. It is patently unlawful for any company to maliciously block FCC-approved Wi-Fi connections.”

In related news, the FCC has slapped Hilton Worldwide with a proposed $25,000 fine for allegedly obstructing the commission’s investigation into claims of WiFi blocking.

Since Nov. 2014, the commission has been trying to investigate complaints that multiple Hilton properties are blocking visitors’ personal WiFi hotspots.

Rather than provide all the information requested by the FCC about all locations involved in the complaints, the hotel company only answered questions about a single Hilton property in Anaheim, CA. Furthermore, notes the FCC [PDF], “Those answers were incomplete and inadequate even for that one property.”

The FCC says it then sent multiple warnings about the inadequacy of Hilton’s response, but has thus far only received “limited information regarding the WiFi blocking systems utilized at a small number of additional Hilton properties and again failed to answer many of the questions.”

Thus, the commission seeks to levy the $25,000 penalty against Hilton for “apparently willfully and repeatedly violating” the FCC order. If the fine isn’t enough to convince Hilton to turn over the requested information, the commission says it is prepared to take further actions against the hotel chain.

“To permit any company to unilaterally redefine the scope of our investigation would undermine the independent search for the truth and the due administration of the law,” explains LeBlanc.

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