One of Minnesota's largest employee unions endorsed former U.S. Sen. Mark Dayton's 2010 bid for governor late Saturday.

Dayton, a Democrat, won the AFSCME Minnesota Council 5 nod over nine other Democratic contenders as well as Republican candidate Patricia Anderson, all of whom screened for the endorsement Saturday.

The AFSCME endorsement, which brings with it the campaigning might of the union, is Dayton's first major endorsement.

"He is in the best position to win this election next fall," said Eliot Seide, executive director of AFSCME Council 5.

He also noted that Dayton has won statewide elections -- to the U.S. Senate in 2000 and to the state auditor's office in 1990. Seide had earlier said that union members would be very interested in candidates' electability as well as their history and their stands on issues important to union members. Democrats have not won the governor's office in Minnesota for more than 20 years.

The heir to the Dayton's department store fortune spent about $12 million of his own money on his 2000 Senate campaign. He retired from the Senate after one term.

He has said he will seed his gubernatorial war chest with his own cash but also hopes to bring in contributions.

Dayton has said he expects to run in a primary whether or not he gets the DFL endorsement next year. That means the AFSCME endorsement may put the union in the awkward position of campaigning for Dayton against the DFL-endorsed candidate, should the party endorse someone else.

Thus far, unions have been split in their endorsements of 2010 Democrats, with no one candidate garnering the nod from multiple union groups.