The IAFF, which originally endorsed Sen. Chris Dodd (D-Conn.), said Thursday that one of the deciding factors in its decision were the votes Obama and rival Sen. John McCain (R-Ariz.) had cast on the collective bargaining agreement that the labor union has been pushing for.

“On every issue important to firefighters, Sen. Obama is and has been in our corner,” Harold Schaitberger, the IAFF president, said. “We can’t overlook Sen. McCain’s service to our country, but we also can’t overlook his poor record on issues critical to the financial security of our 290,000 members.”

Obama was set to accept the endorsement by video message to the 3,500 IAFF members gathered at their summer convention in Las Vegas.

Another former candidate and a potential running mate for Obama, Sen. Joseph Biden (D-Del.), is scheduled to address the group on Obama’s behalf.