A class action lawsuit on behalf of about 700 Guatemalans who were subjected to syphilis experiments by American doctors in the 1940s will be filed against the U.S. government in three days unless reparations of some kind are made to their families, plaintiffs attorneys said Tuesday.

The Obama administration apologized last October for U.S. government doctors infecting Guatemalans with the syphilis virus from 1946 to 1948 to study how the sexually transmitted disease is passed and whether penicillin treatment was effective. The experiments came to light in 2009 through research by historian Susan Reverby, a professor of women and gender studies at Wellesley College in Massachusetts.