At issue, according to the 38 page complaint released as a PDF today, are basic elements of the Linux operating system licensed under GPL V. 2. The complaint says Cisco's Linksys unit failed to provide source code.
This is the first time the FSF has had to go to court for relief in its 15 years. Previous violations, mainly over Bruce Perens' Busybox, were filed through GPL Violations and settled out of court.
As noted earlier this is not the first time Linksys, which Cisco acquired in 2003, has been accused of a code violation. When I researched the 2003 case sources told me Linksys was running very independently of Cisco.
UPDATE: Perens was an original author but writes the suits were filed by later developers. Also, GPL Violations was not involved in the initial complaint against Linksys.
That may still be the case. But five years on this is no longer an excuse, just an explanation. Cisco may have defenses in fact, and it may seek to argue the law.