Retaliation is employer "payback", a low-down way to punish employees for reporting poor work conditions, employer wrong-doing, etc. The risk to the retaliating employer could include a new charge brought against them or even a lawsuit against the employer.
In 2010 for the first time ever, retaliation was the most frequently filed charge with the EEOC. Of the over 99,000 charges filed, retaliation under all statutes totaled 36,258. Historically, race had been the most frequently filed charge since the EEOC became operational in 1965.