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.
New Hampshire is the site of the first presidential primary next year, and the TPP has already become an issue on the campaign trail.
"Politics as usual has not worked. It's time for a political revolution."
"AFSCME members want a candidate who is committed to fixing our out-of-balance economy and raising incomes for working people."
"I am incredibly proud that there is finally a candidate speaking to the values I've held my whole life," said one worker.
Clinton and Sanders largely agree on issues ranging from labor law reform to rebuilding infrastructure to changing education law.
The endorsement came after Clinton - and only Clinton - addressed the NEA's board for an hour and a half.
Carpenters president Douglas McCarron introduced Clinton as "the next president of the United States."
The Letter Carriers endorsement is important, as the union has members in every state in the U.S., plus Puerto Rico, Guam and the U.S. Virgin Islands.