The buying practices of supermarket chains Coles and Woolworths should change overnight, according to federal agriculture minister Peter McGauran says, reported the Australian Broadcasting Corporation.

McGauran said a long-term partnership should be formed between the growers and the supermarkets so that rural Australia is globally competitive.

"We will be part of an industry-grower-government partnership, but we've got an immediate problem that won't be solved over the long-term because they simply won't still be in business," he said.

"Consequently country of labelling is important and the buying practices of the supermarket chains have to change overnight to support growers."

McGauran's comments come as a group of about 25 Tasmanian farmers continue a tractor trek to Canberra in Melbourne today, lobbying for tougher country of origin food labelling laws and an end to imports.

The 'fair dinkum food' campaign was launched after Tasmanian farmers suffered major contract cuts in the pea and potato sectors.