WASHINGTON  A group of liberal bloggers said it was teaming up with organized labor and MoveOn.org to form a political action committee that would seek to push the Democratic Party further to the left.

Soliciting donations from their readers, the bloggers said they were planning to recruit liberal candidates to challenge more centrist Democrats currently in Congress.

The formation of the group is another step in the evolution of the blogosphere, which has proven effective at motivating party activists to give money and time to political campaigns, especially in local races.

But it also illuminates a deepening wrinkle for President Obama, whose attempt to build a broad governing coalition  often by tempering some of his more liberal positions  has already angered some of his supporters on the left.