From Libertarian Wiki

Affirmative action means giving someone a preference or advantage based on the color of his skin, or gender, to reverse the effects of discrimination and often for political motivation. Quotas are an extreme form of affirmative action.

The original concept of affirmative action, when introduced by the Johnson administration, was that it is desirable to not merely act on non-discrimination passively (i.e., saying "this job is open to any applicant", but then making no efforts to find minority applicants), but should also be done actively, by taking definite actions to find applicants from minorities.

This would be, in its way, admirable. However, in current use, affirmative action goes beyond this, often mandating the use of quotas for setting aside jobs or a portion of college entrance positions for each minority (including also some so-called minorities that are actually majorities).