Woolworths workers picket distribution centre in Melbourne as ...

Woolworths and the union representing striking workers have begun negotiations, as about 200 staff picket a major warehouse in Melbourne's south-east.

Members of the United Workers Union (UWU) are locked in an an industrial dispute with the supermarket giant over pay and conditions.

The dispute has interrupted work at four distribution centres, leading to some empty shelves at Woolworths supermarkets across Melbourne.

The distribution centre closures have affected supplies at supermarkets across Victoria and New South Wales, including this store at Albury. (ABC News)

Woolworths said on Sunday it was planning to reopen its distribution centre at Dandenong South on Monday morning, prompting UWU members to gather at the site.

The workers are attempting to block three entrances to the distribution centre.

Woolworths said the reopening of the distribution centre would improve the availability of items such as nappies, toilet paper and drinks on its supermarket shelves.

"We know that there have been shortages on our shelves in some Woolworths stores and that this is really frustrating for our customers," a Woolworths spokesperson said in a statement.

There's been a shortage of items at some Woolworths supermarkets due to industrial action. (ABC News: Brian Hurst )

"We sincerely apologise for the inconvenience and would like to thank our customers for their understanding and for treating our teams with respect."

Woolworths said it would continue to negotiate with the UWU and requested that the union allow "safe passage for our team wishing to return to work" at the Dandenong South distribution centre.

The UWU accused the supermarket giant of caring "more about profits than workers' safety" as the industrial dispute stretched past its 11th day.

Central to the UWU's concerns is the productivity "framework" warehouse staff are subject to during shifts.

Hundreds of workers at Woolworths distribution centres have stopped work indefinitely in recent weeks. (Supplied: Woolworths)

The union says the framework, which requires warehouse staff to achieve a 100 per cent performance target when picking up items at speed, is "dangerous, inhumane and unsafe".

"We have raised it in meetings, and we have raised it on the shop floor: treating workers like robots is unacceptable, and addressing the framework is the first priority of our members," UWU national secretary Tim Kennedy said.

"The fact we have not reached agreement around this issue after 11 days of strike action suggests one of the country's largest private-sector employers cares more about profits than workers' safety."

UWU members have been taking industrial action against Woolworths for more than 11 days. (ABC News: Stephanie Ferrier)

Woolworths disputes the UWU's characterisation of the framework, saying it was developed "with safety as an inherent component … [and] to ensure a fair approach to operational performance".

"The framework has been developed based on the time it should take a person with reasonable skill, applying reasonable effort, working at a safe and conscientious pace, that can be maintained for the duration of a shift, to complete a task," a Woolworths spokesperson said.

The union also accused Woolworths of bad faith by reopening its distribution centre before it was due to meet again with union representatives this morning.

Woolworths said the majority of those contacted at the distribution centre wanted to return to work.

It also said another union — the Shop, Distributive and Allied Employees' Association (SDA) — had endorsed a pay offer from Woolworths last week.

The supermarket said the UWU was seeking an immediate pay increase of 25 per cent, with wage increases of 15 per cent in years two and three of the agreement.

It said that demand came "at a time when Woolworths is actively working to keep food and groceries affordable for our customers who are facing cost of living pressures".

A UWU spokesperson told the ABC the negotiations covered workers on a range of pay scales and different pay increases were being sought for different workers.

The UWU said the agreement Woolworths reached with the SDA was irrelevant.

"The other union referred to by Woolworths, which largely represents retail workers, has less than 10 members affected by the framework in this dispute, compared to the 1,500 United Workers Union members on strike," Mr Kennedy said.

"Workers are fighting against Woolworths' extreme framework, and UWU will continue to back in members and fight for what is important to workers."