Terminated older (over age 40) workers who receive severance packages will find themselves presented with a long document that includes, among other things, a release of any legal rights they may have against their employer. Those releases — or "waivers" in the parlance of federal law — are governed by the Older Workers Benefit Protection Act [OWBPA]. The OWBPA contains detailed requirements that the employer must satisfy for their waivers to hold up in court.
Over time a few ex-employees have been able to convince courts to void their releases, which allowed them to sue their ex-employers despite seeming to have signed away their rights.
The linked decision of the federal District of Minnesota in Pagliolo v. Guidant Corporation is a virtual road map to attacking a release under the OWBPA. The opinion is methodical, and there's a lot to be learned here for both ex-employees and downsizing employers (and their attorneys).