Leaders of the Working Families Party are mulling over contesting the Phildelphia, Pennsylvania city-council at-large seats. Generally the Working Families Party doesn’t organize in states unless those states permit fusion. Pennsylvania doesn’t permit fusion, except in a very limited manner, but Philadelphia does have a provision that makes it possible for a party with less than majority support to win seats on the city council. That is attractive to the Working Families Party. See this story.
The Phildelphia provision, like similar provisions in Washington, D.C., and in some cities in Connecticut, makes it impossible for any party to run for all the available at-large seats. That leaves an opening for parties who aren’t the dominant party in the city to win some seats.