The powerful SEIU Local 1021 union and an influential Oakland advocacy group last month sent scathing letters to members of the Alameda County Democratic Central Committee in an effort to block the endorsement of Oakland District 2 Councilmember Abel Guillén.

Just days before the central committee is set to make a decision this Saturday for the race between Guillén and challenger Nikki Fortunato Bas, the incumbent’s backers are pushing an intense lobbying effort on his behalf.

While SEIU Local 1021 is harboring great resentment toward Guillén for a perception that he stymied their efforts during labor negotiations last winter with the city, other unions appear to have a different view of the first-term councilmember. Guillén had previously received strong support from union labor.

“Oakland City Councilmember Abel Guillén has been that champion for us on the Oakland City Council,” Building and Construction Trades Council Secretary-Treasurer Andreas Cluver wrote this week to central committee members.

“Whenever we have needed Abel to come through the Building Trades, he has taken that stand, often when he is the minority on council to stand with us.”

Two weeks ago, Guillén received support from the Oakland Firefighters union Local 55.

“It’s always a disappointment to me when Labor goes in different directions during a vote or an endorsement. But I also recognize that democracy is messy, ” wrote Zac Unger, vice president of the Oakland International Association of Firefighters Local 55.

“When it comes to Abel Guillén, I can only speak to what Oakland’s firefighters have seen. In the experience of Local 55, Abel  has been a staunch ally.”

There are late signs that the lobbying effort on Guillén’s behalf might be making some headway with central committee members. According to those familiar with the horse trading leading up to Saturday’s endorsement meeting in Oakland, Guillén is assured of at least a “no endorsement” in the two-person race, and may likely win the party’s critical backing.