Here's the deal ... NFL Network's Tom Pelissero says Kemah Siverand attempted to dress up a female companion like a Seahawks player in an attempt to get her past security and into his room.

The problem? Pelissero says Siverand's plan was all caught on camera ... and with Pete Carroll implementing a bubble-like atmosphere for the 'Hawks -- that's a big no-no.

Pelissero says the Seahawks busted the hell out of Siverand's little operation -- and fired him for putting the team at risk of a coronavirus outbreak.

Pelissero adds the cut was meant to send a message to both Siverand and Seattle's entire roster ... saying, "Put the team at risk, suffer the consequences."

Of course, the decision to fire Siverand was a pretty easy one ... the cornerback was an undrafted free agent who had little chance of making the roster anyway.