Time for a definitions game.
Blackmail is the act of threatening to reveal substantially true information about a person to the public, a family member, or associates unless a demand is met. This information is usually of an embarrassing, socially damaging, and/or incriminating nature. As the information is substantially true, the act of revealing the information may not be criminal in its own right nor amount to a civil law defamation; it is the making of demands in exchange for withholding the information that is often considered a crime.
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18 U.S.C. § 873 states, "Whoever, under a threat of informing, or as a consideration for not informing, against any violation of any law of the United States, demands or receives any money or other valuable thing, shall be fined under this title or imprisoned not more than one year, or both."
Copyright infringements are in violation of copyright law.
These lawyers have, as a consideration for not informing the courts, demanded money as a settlement from alleged copyright violators.
I'd say this is pretty much exactly the definition of blackmail.