WASHINGTON — One little-noticed but fascinating cleavage in labor’s political effort this year is the battle between the AFL-CIO unions and those belonging to Change to Win.

The former have been split among the various candidates, with the largest chunk going to Hillary Clinton and John Edwards, while Barack Obama has also drawn support. A number of state branches have gone their own way, sometimes differing from the international union they belong to. Meanwhile, the AFL-CIO as a whole has remained neutral, despite some ferocious internal struggles led by unions favoring Clinton, particularly before the Ohio primary.

The AFL-CIO chose to remain on the sidelines, but Clinton won Ohio anyway. Speaking of Ohio, just before it several Change to Win unions — including the Teamsters and the Service Employees International Union — backed Obama, saying they would be able to push him over the top. The Change to Win federation also joined his team. Those unions, particularly the Teamsters, are strong in Ohio — but Clinton won easily.

Intriguingly, when the Change to Win federation was formed in St. Louis in the fall of 2005, one factor was the desire of SEIU and its fellow unions to focus on organizing instead of politics. But now, a political battle within labor is increasingly taking shape — though all is likely to be patched over once the Democrats settle their nominating battle.