If residents of metropolitan Melbourne and Mitchell Shire leave their house for one of the four allowed reasons without a mask or face covering after Wednesday, they could be hit with a $200 penalty.

But the new mandate presents challenges for certain people and there is concern around supply.

Council to Homeless Persons chief executive Jenny Smith said simply buying a mask and wearing it was not straightforward for everyone.

"A lot of vulnerable people in the community are not in a position to watch the news all day, and might not realise that wearing a mask is a new requirement. Most will struggle to afford masks and not be in a position to make a mask," she said.

Ms Smith said instead of issuing fines, police should be able to offer masks to those who don't know about the requirement or who are unable to buy one.

Chief executive of autism advocacy group Amaze, Fiona Sharkie, said some people with autism would have difficulties wearing masks or face coverings, particularly those with related sensory sensitivities or communication challenges.

"Wearing masks when we go outside our homes is a big change for everyone, but our community is committed to working together to do our bit in trying to limit the spread of coronavirus," Ms Sharkie said.

Asylum Seeker Resource Centre chief executive officer Kon Karapanagiotidis said while he supported the call for mandatory masks, there was further anxiety within the refugee community.

"What we're worried about with masks becoming mandatory is you're going to see lots of vulnerable people not leaving the house for essential services, because they don't have the means," he told AAP.

"Multicultural communities already face massive inequality when it comes to accessing health literacy, massive inequality when it comes to things like personal protective equipment, which is a luxury to be able to even access."

Launch Housing chief executive officer Bevan Warner told AAP on Monday they had started stockpiling masks for people experiencing homelessness, and noted that the new rule revealed just how vulnerable some groups were.

"In a sense, the mask is a point in time distraction from their real exposure to risk, which is that it is impossible to genuinely self-isolate or to live a productive and dignified life without a home," he said.

Mr Karapanagiotidis said charities were on the front line of aiding disadvantaged communities during the pandemic and more needed to be done to support them and the people they help.

"We're going to need tens and tens of thousands of masks, which charities shouldn't have to pay for themselves, or beg people to donate them," he said.

"We're actually trying to deliver public health ... we're trying to keep the community safe."

Australian Associated Press