silent treatment

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Maintenance of aloof silence toward another as an expression of one's anger or disapproval.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A form of social sanction that consists of ignoring a particular individual, neither speaking to that person nor responding to his or her words.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an aloof refusal to speak to someone you know