[adenner]

Not really, they are using the 2.4GHZ ISM band. It may be legal (INAL) as long as you are not interfering with any licensed use of the band and are not violating FCC Part 15 Rules. (http://www.afar.net/tutorials/fcc-rules)

Still not cool though...

[nitrogen]

Transmitting deauth packets is illegal according to cases involving hotels and conference centers jamming wifi hotspots.

https://en.wikipedia.org/wiki/Wi-Fi_deauthentication_attack

[Natanael_L]

IIRC that's more a case of blocking ALL networks vs blocking networks that imitate yours.