Four former IBM employees over age 55 sued the company Wednesday in what plaintiffs lawyers say is a potentially major age-discrimination lawsuit, alleging that top executives “took the calculated risk of openly breaking the law” to cover up massive, targeted layoffs of older workers.

The former workers, in a federal lawsuit focused on alleged company violations of the Older Workers Benefit Protection Act and the Age Discrimination in Employment Act, say they are just four of more than 20,000 IBM employees over age 40 who’ve been discharged during the past six years as the company secretly looked “to correct seniority mix” by replacing baby boomers with recent college graduates and other tech-savvy young workers.