The son of the Fire Department commissioner, Salvatore J. Cassano, resigned on Monday from his job with the department after a series of offensive Twitter posts, many of them racially inflammatory, surfaced.

Joseph Cassano, 23, who joined the department as an emergency medical technician in October 2012, came under fire for posts that suggested a hatred for Jews, blacks and poor people.

Commissioner Cassano expressed both disappointment and love for his son, adding that the decision to resign was the right one.

“I am extremely disappointed in the comments posted online by my son Joseph, which do not reflect the values — including a respect for all people — that are held by me, my family and the F.D.N.Y.,” the commissioner said in a statement released Monday afternoon.