Under scrutiny from the Australian Competition and Consumer Commission for potential breaches of competition laws, Woolworths says it is not as big and bad as people think and is under pressure from German chain Aldi.

Last year, Woolworths opened its biggest supermarket in Australia at Majura Park to compete with Costco, while Coles opened an even bigger one at Gungahlin.

Canberra-based Supabarn spokesman James Koundouris said the ACCC's 2008 grocery inquiry noted Coles and Woolworths accounted for about 70 per cent of grocery sales in Australia and 50 per cent of fresh product sales.

In the larger stores segment, that dominance was even more pronounced. Mr Koundouris said Woolworths was lumping in smaller shops to bolster a case of having less dominance.

''I don't believe that pulling together supermarkets with other food retailers such as fast food, bakery and delicatessens is a true indication of a supermarket operator's market share,'' he said.

A spokeswoman for Woolworths said she could not comment on market share in the ACT. ''We haven't got jurisdictional market share numbers.'' Aldi only responds to media inquiries which are mailed to their Australian headquarters. Although an ACT administrative tribunal found Woolworths was trading in breach last year of its lease at Bonner, exceeding the permissible 1500 square metres by about 140 square metres, it decided not to take any more action.

Matthew Farrah said on Tuesday that Woolworths expansion at Bonner had ''killed'' his supermarket business at Forde. ''There's no business, there's no growth.''

A floor space graph in the Martin report in 2011 prepared for the ACT government showed major supermarkets planning to double their space in the ACT market, with Coles and Woolworths towering over rivals.

The select committee on ACT supermarket competition policy noted Aldi had turned down two direct sales of land at Kaleen and Wanniassa, reflecting their position that their retail niche market was saturated.