The American Federation of State, County and Municipal Employees, AFSCME, spent some $2 million backing Clinton, whom the union endorsed, and then took out a $1 million bank loan in February to replenish its political war chest.

"When we endorse a candidate, we back it up with everything we've got," said AFSCME President Gerald McEntee.

The Washington Times said McEntee is a longtime ally of both Sen. Clinton, D-N.Y., and former President Bill Clinton – and that has raised questions among union officials as to the wisdom of sticking with her until the presumed bitter end.

AFSCME spent $200,00 on a negative mailer about Barrack Obama during some of the early primaries. The national union also has continued to stump for Clinton in Tuesday's Oregon primary despite requests from state union leaders to back off.

Oregon AFSCME officials said in a letter to state members that the spending on Clinton's behalf was "disrespectful" and "probably meaningless," The Times said.