The retail group that owns Rebel Sport, Supercheap Auto and Macpac says it underpaid store managers by about $32 million over the past six years by not applying overtime rates properly.

Super Retail's chief executive, Peter Birtles, who was due to stand down as CEO on March 31, said he would bring his departure date forward to February 20 in recognition of the "significance of this underpayment".

Super Retail boss Peter Birtles said he would stand down as CEO a month early. Credit:Daniel Munoz

“We are very disappointed that we have let these team members down and not met our standards,

and we apologise to each person affected unreservedly," Mr Birtles said.

Super Retail Group, which also owns the Rays Outdoors and BCF retail chains, said on Tuesday a recent review of its employment arrangements had uncovered the underpayments, which affected about 3000 current and former employees.