Uriah Heap, Belafonte, Rose and all others credit Hellerman and Minkoff.
Some dates:
Bikel, Hellerman and The Big Three recorded it in 1964; the Weavers and Judy Collins in 1963; Rose in 1967, and Uriah Heap in 1970. These dates may not be firsts, I haven't checked but just noted dates of albums still listed. Others included UFO, Velvet Fogg, Bobby Gentry.
Hellerman included it on his protest album, "This Land is Your Land: Songs of Social Justice, UAW;" The Weavers in "Reunion at Carnegie Hall, 1963."