Residents cannot get to their cash because two post offices on their estate keep running out of money.
Some people have been left without pensions and benefits because of the shortage.
Laurence Townsend, Brighton and Hove City Council community participation and policy officer, has written to Consignia, the company which runs post offices, to complain.
The problem has arisen on the Whitehawk estate in Brighton, where there are sub-post offices in Whitehawk Way and Whitehawk Road.
Residents first aired their complaints about the cash shortage at a meeting of the Whitehawk Community Forum in December.
Maggie Smeeth, who has lived on the estate for 34 years, said: "A couple of weeks ago I went to the post office on a Monday and stood outside waiting for about 45 minutes because we can't all go in at one time.
"When we could go in, we waited for about 15 minutes to be told they had run out of money. It's the first time I have ever had that happen."
Mrs Smeeth said many parents on the estate liked to collect their pensions or benefits while taking their children to school so they could go straight off to do their shopping.
But with both offices running out of money at various times, people were trekking to nearby Kemp Town - until the sub-post office in St George's Road closed unexpectedly at Christmas.
Councillor Mo Marsh said: "Consignia must have some kind of indicator as to the amount of usage the offices get.
"I can't understand why Consignia can't make funds available, particularly as the post office in St George's Road is closed."
There was no one available to comment at Consignia.
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