Who were these wicked dwarves?

[Aganzir]

Alas, it seems probable that (as Men did later) the Dwarves of the far eastern mansions (and some of the neared ones?) came under the shadow of Morgoth and turned to evil.

Tolkien's note on Of Dwarves And Men, The Peoples of Middle-earth

Also in some writings the Noldor believed the dwarves would smith to the highest bidder, including Morgoth.