Prefixes (such as anti, co, inter, non, re, un) as a general rule should not be hyphenated. The exceptions tend to be for clarity — for example, to break up repeated vowels (anti-inflammatory) or minimize confusion (re-creation, as opposed to recreation). But do use hyphens with capitalized words (anti-American) or dates (pre-2000), or if the prefix is part of a multiword concept (non-load-bearing wall). Also hyphenate if the prefix stands alone (over- or underutilized asset). Written Work recommends checking out the exhaustive Table 6.1 in The Chicago Manual of Style, 14th edition, for everything you could possibly want to know about prefixes, suffixes, compound words, and hyphenation — including exceptions to the rules.