Current primary backer of Erebus Motorsport's #4 Mercedes, IRWIN Tools, will exit the category at the end of the season.
The news has followed quickly after Friday's announcement that SP Tools will move its support from Erebus to the Holden Racing Team from 2014.
IRWIN Tools has been a single car primary sponsor in V8 Supercars since 2007.
Spending its first two years at Britek Motorsport with drivers Alan Gurr and Marcus Marshall, the Newell Rubbermaid brand moved to Stone Brothers Racing for 2009, coinciding with the arrival into the team of Alex Davison.
Lee Holdsworth took over the car last year, with the sponsorship continuing into the team's first season as Erebus.
“Our original relationship with Jason Bright's Britek operation, Stone Brothers Racing and more recently Erebus Motorsport V8 has delivered significant value to our brand and customers,” said IRWIN's head of marketing, Tom Veale, in a statement.
“While V8 Supercars has been highly successful in growing the IRWIN brand, it is time to redirect our efforts towards meeting other brand and business objectives.”
An IRWIN backed car has yet to win a V8 Supercars race, with just five opportunities now remaining across the Phillip Island and Homebush events.
Holdsworth currently sits 20th in the points standings having scored a strong fifth in the Pirtek Enduro Cup alongside Craig Baird.