Members of the Communication Workers Union (CWU) from the Severn Street depot in Welshpool mounted picket lines on Wednesday, joining other Royal Mail offices in striking over pay and conditions.
Around 13 workers took to the street, waving a banner as motorists honked their horns in support and members of the public wished them well.
The dispute is over a two per cent pay rise.
Danny Edwards, union rep for Welshpool's delivery depot, said the pay and change to conditions being proposed would mean a lot of workers would actually receive less.
Mr Edwards, who has worked in the mail industry for more than 35 years, said: "It's great working for the post normally, but it's getting quite stressful now. We can't really afford to go out on strike, especially for two days next week. But we feel if we don't take a stand at some stage we'll be rode over roughshod.
"We've had an awful lot of support from the public. If you don't keep the public with you, you're onto a loss straight away. The shareholders don't seem to care about the public.
"Welshpool Town Council came out and said they were supportive of us. I think we could lose rural services if we're not careful. You don't realise what you've got until it's gone."
CWU said more than 100,000 workers were involved, making it the biggest strike of the summer and follows a walkout last Friday, with further stoppages to take place on Thursday, September 8 and Friday, September 9.
CWU general secretary Dave Ward said: “There can be no doubt that postal workers are completely united in their determination to secure the dignified, proper pay rise they deserve.
“We can’t keep on living in a country where bosses rake in billions in profit while their employees are forced to use food banks.
“Postal workers won’t meekly accept their living standards being hammered by greedy business leaders who are completely out of touch with modern Britain.”
A Royal Mail spokesman said: “The CWU’s self-centred actions with the wider trade union movement is putting jobs at risk, and making pay rises less affordable.
“Each strike day makes that more difficult, making Royal Mail’s future more uncertain than at any time in its long history.
“The CWU has failed to respond to our latest invitation to meet to discuss change and pay, instead creating red herrings on the Universal Service, re-nationalisation and shareholder activity.
“The CWU is deflecting to avoid talking about the changes we need to make as a business.
“We remain ready to talk with the CWU to try and avert damaging industrial action and prevent significant inconvenience for customers. But any talks must be about both change and pay.”