The relevant policy is at http://en.wikipedia.org/wiki/Wikipedia:Blocking_policy#Disruption, which says in part:
"Sysops may, at their judgement, block IP addresses that disrupt the normal functioning of Wikipedia. Such disruption is to be objectively defined by specific policies, and may include changing other user's signed comments or making deliberately misleading edits. Users should be warned that they are violating policy before they are blocked."
And, BTW, the warning has now become a discussion. See: http://en.wikipedia.org/wiki/User_talk:Netoholic#Warning_re:_refactoring and http://en.wikipedia.org/wiki/User_talk:Netoholic#refactoring for the previous discussion that led up to this.
Thanks, Brian (BCorr)
Phil Sandifer wrote
What portion of the blocking policy are you invoking in this warning?
-Snowspinner