Woolworths bears responsibility for the empty shelves seen in supermarkets across parts of Australia by attempting to treat workers like “robots”, the head of the Australian Council of Trade Unions has said, as a strike of warehouse workers extends into a second week.

Up to 1,500 employees began rolling 24-hour strikes on 21 November in warehouses in New South Wales and Victoria, seeking improved wages and safety. One of the major issues is a new framework system employed at the warehouse that tracks workers down to the minute, and logs performance each shift using an algorithm.

This week the strike extended to six sites in three states with workers at the Queensland Heathwood distribution centre joining the strike. Lineage, a cold storage warehouse that supplies Woolworths stores out of Melbourne, also began striking this week over improved pay and conditions.

The strike has resulted in bare shelves in stores across at least two states in the past week.

Guardian Australia observed in one Melbourne CBD Metro location this week that there was no supply of cold drinks, with a sign in the store advising of delays due to industrial action.

The United Workers Union secretary, Tim Kennedy, said bare shelves were now seen across the eastern seaboard.

“We warned that this would happen if five warehouses took strike action,” he said. “Woolworths knows how to fix this, and now is the time as families start their Christmas preparations.

“Workers do not want to feel pressured to cut corners and work unsafely for fear of losing their job. Woolworths must prioritise the safety and wellbeing of workers above all else.”

A spokesperson for Woolworths confirmed there was “limited stock flow” in some stores in Victoria, NSW and the ACT.

“All stores are still receiving regular deliveries of stock, in some cases at a reduced frequency,” the spokesperson said. “Not all stores are impacted and the degree of stock flow challenge varies from store to store.

“We have extensive contingency plans in place to minimise any ongoing impact to customers, ensuring regular deliveries to stores utilising the other 20 DCs [distribution centres] and 8,000 team members in our network.”

A further bargaining meeting was held with workers on Friday and the Australian Council of Trade Unions secretary, Sally McManus, visited striking workers at the Erskine Park site in NSW.

“Woolworths is to blame for any shortages,” she said. “Workers want a safe workplace and that means the company has to withdraw the systems they’ve put in place that basically treat workers like robots.

“They’re not robots, they’re flesh and blood human beings that have bills to pay and have families and they absolutely deserve their safe workplaces and any system that they want to bring in that treats them like robots is going to be rejected by human beings.”

The Woolworths spokesperson said the company was working to resolve the dispute so workers could receive new pay rates before Christmas.

“We have already put forward several offers with competitive pay that is above industry standards, above local market rates, above inflation, and well above the award.”