IBM is defending itself from the latest round of accusations about its firing practices. Months after a ProPublica report said the technology giant had dismissed more than 20,000 workers older than 40 in the last five years, IBM is facing fresh claims of discriminating against employees based on their age.

A class-action lawsuit filed in Manhattan federal court on behalf of three former IBM employees alleges the company discriminated against them due to their age when the company fired them, Bloomberg reported.

The suit draws on the ProPublica report which detailed systematic breaking of age-discrimination rules by IBM as it strove to prune its workforce in high-wage areas and rebuild a younger base of employees.

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"Changes in our workforce are about skills, not age," a spokesperson for IBM emailed CBS MoneyWatch. "In fact, since 2010 there is no difference in the age of our U.S. workforce, but the skills profile has changed dramatically. That is why we have been, and will continue, investing heavily in employee skills and retraining — to make all of us successful in this new era of technology."

The suit filed on Monday echoes claims by Jonathan Langley, a 60-year-old former salesman at IBM in Austin, Texas, who filed suit against IBM in May, saying he'd been forced out after 24 years as a "successful employee" because of his age.

IBM employs almost 400,000 people worldwide, including tens of thousands in the U.S.