RoseAnn DeMoro, executive director of the National Nurses Union, said that for her union, for now at least, it's "Bernie or Bust."
The federation is holding off on an endorsement at this time while some of its unions work for Clinton and others for Sanders.
However, major unions that are part of the federation have already endorsed Clinton while others have come out for Sanders.
Have Donald Trump's promises played like the sound of music to the ears of American workers?
In Des Moines, Iowa, it was much more like a fundamentalist Christian revival meeting than a political rally.
One unionist said, "I like Bernie. I like what he has to say, but I think Hillary is far and above in knowledge."
Richard Trumka remarked, "We deserve better" than Donald Trump's racism.
"Sanders stands with working families against corporate greed, Wall Street, and the big banks, and we are going to help him."
The SEIU board voted on Nov. 17 to endorse former Secretary of State Hillary Clinton for the Democratic presidential nomination.
Workers at the IKEA warehouse in Stoughton, Mass., were forced to strike on Nov. 16.