An announcement from Plus Fitness has cited a contractual dispute between the Russell camp and Erebus as the reason for the split.
Erebus had been running Russell under its second Racing Entitlements Contract this year in a deal that saw the Novocastrian bring his sponsor and an ex-Walkinshaw chassis to the table.
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The contractural dispute is understood to centre around payments for the preparation of the car, which is run alongside Erebus' main entry for David Reynolds.
Erebus' deal with the Russells is said to include a provision for the team to continue to use the Holden for the remainder of the year in the event of a contract termination.
With the REC rules requiring Erebus to field the entry at this weekend's Coates Hire Ipswich Super Sprint, the team is currently in talks with other sponsors and drivers that can take over from Russell.
Dunlop Series runner Shae Davies, who is already scheduled to co-drive the car in the Pirtek Enduro Cup, is strongly tipped to step in.
The split with the Russells follows a fracas between Erebus owner Betty Klimenko and Plus Fitness boss John Fuller over a sponsorship activation being undertaken in the Townsville paddock.
Stressing the company's support for the Russells, Plus Fitness' statement said that the Townsville disagreement contributed to the withdrawal.
“Plus Fitness Racing has decided to withdraw its sponsorship with AR Racing and car #4 from the 2016 Supercar Championship due to ongoing contractual disputes between AR Racing and Erebus Motorsports,” read the statement.
“AR Racing (The Russell's) informed John Fuller from Plus Fitness of their decision to terminate the arrangement with Erebus therefore as their main Sponsor Plus Fitness have decided to support The Russell's actions and also withdraw.
“A key determining factor for Plus Fitness in sponsoring a Rookie Driver in a Low Ranking Team was to rely on back of garage track activations.
“Plus Fitness have been restricted from doing this due to factors outside of their control and for reasons they believe are due to the relationship between AR Racing and Erebus Motorsport.
“This has also impacted on their decision to withdraw.
“Plus Fitness Racing is currently reviewing its commercial arrangements with Erebus and car #9 and driver David Reynolds will remain a Plus Fitness Brand Ambassador for the remainder of the 2016 season.
“Plus Fitness Racing is committed to its involvement in Motorsport and is currently looking at options for the remainder of the season and beyond.”
Erebus Motorsport has been contacted by Speedcafe.com for comment.