Service Employees International Union (SEIU), one of the largest and most powerful labor unions in the country, is slated to elect not only their first woman president, but also their first openly gay leader.

Mary Kay Henry, an out lesbian, has secured the support of several large local unions and is poised to receive support from the giant New York-based local union, which represents nearly 15% of SEIU’s total membership.

If elected, Henry would represent 2.2 million union members.

Politico reports:

A giant New York-based local union is poised to vote to support California labor leader Mary Kay Henry (above) for the presidency of one of America’s largest unions today, three sources familiar with the union said, dealing a stunning rebuff to Service Employees International Union President Andy Stern and his handpicked successor, Anna Burger.

With some 300,000 members — about 15% of SEIU’s total membership — 1199 is the largest of the constituents of SEIU whose local leaders are now voting in an election that pits Burger’s promise to continue SEIU’s high profile role as powerhouse of Democratic Washington politics and Henry, whose backers hope that she’ll defuse tensions between SEIU and other unions and return it to a more traditional role of organizing and representing members.

The election is, in traditional political terms, a choice between Burger’s promise of continuity and Henry’s promise of change, and change appears to have the upper hand.