Firms including Crawford and Cunningham Lindsey face a fight to remain on Ecclesiastical's loss adjusting panel.
The insurer announced this week that it is to cut the number of firms on the panel as part of a "complete supply chain review".
But it insisted its motivation is to improve customer service rather than reduce costs.
Brian King, public affairs manager at Ecclesiastical, said: "We will work with fewer loss adjusters, but what we will offer is a more in-depth insurer.
"This is in line with the FSA's Treating Customers Fairly initiative, since we will require our adjusters to have specialist knowledge and be proactive."
He added that other suppliers such as repairers would also be reviewed.
King said: "Cost is not the reason for this. We could end up spending more if we can improve our service."
It is understood that Ecclesiastical currently works with around 10 adjusting firms, and that the review will cut the amount of firms down to six or less.
Another adjuster known currently to be on the panel is Carr Greenwood Smith.
King said a formal process for the review had not yet been decided, but that existing adjusters would need to show levels of competence in Ecclesiastical's core business areas, such as churches and care homes.
The view will be completed by the end of the year.
