Donna Edwards, center, a contender in the race for Prince George’s county executive, greets spectators during a parade down Addison Road on May 5 in Seat Pleasant, Md. (Bill O’Leary/The Washington Post)

Service Employees International Union (SEIU) Local 500 is backing Donna F. Edwards in her bid to be the next county executive of Prince George’s, citing her advocacy on behalf of working people.

Mark McLaurin, the political director for SEIU Local 500, which has 15,000 members statewide, said the group has confidence in Edwards to “clean house” in the county’s struggling public education system and focus on improving its early-education programs.

The union, which is leading a campaign to oust Senate President Thomas V. Mike Miller Jr. (D-Calvert) and his “lieutenants,” thinks electing Edwards would be a “body blow” to the Democratic establishment, McLaurin said. Edwards is campaigning as a political outsider and in forums has linked her leading opponent, state’s attorney Angela Alsobrooks, to the county’s Democratic elite.

“We are confident in Donna’s ability and commitment to fighting the ruling powers that be and operating in the interests of working people,” McLaurin said.

The other candidates vying for the Democratic nomination — which in heavily Democratic Prince George’s is tantamount to winning the election — are Alsobrooks; state Sen. C. Anthony Muse (D-Prince George’s); Obama appointee Paul Monteiro; former lieutenant governor Samuel W. Bogley III; Lewis S. Johnson; Billy Bridges; Michael Kennedy; and Tommie Thompson.

Edwards’s campaign also unveiled an online advertisement Monday that includes supporters highlighting her commitment to education and job training. The segment will appear on social media in targeted advertisements, her campaign said.

The primary is June 26.