SEIU is going to bat for Martha Coakley in Tuesday's special election primary in Massachusetts.

The union launched a radio ad buy Thursday totaling $214,000 in the Boston area, according to a source. The spot is a 60-second bio ad for the state Attorney General, who is favored in the Democratic primary for Sen. Ted Kennedy's (D-Mass.) seat.

Rep. Michael Capuano (D-Mass.) is making a late charge at Coakley, but the SEIU's investment is significant and should give Coakley a boost. It is also a sign that important groups don't think the race is over yet.

The meat of the ad states: "As Attorney General, she cracked down on subprime mortgage lenders and recovered more than six hundred million dollars in taxpayer money related to the Big Dig. She protected consumers from unfair and deceptive trade practices by big health insurers. And she led efforts to make sure President Obama’s economic recovery money goes to creating jobs and improving the economy for working families in our state, not the special interests."