One owner claims business got so bad he had to close.
Another says he will stay for a further three months, but if business does not improve, he too will close down.
The four businessmen, based in Oswald Street, claim they were given no warning when the structure was moved from the RAC building before it was demolished.
Nejdet Ozbek, 39, the owner of Teacup coffee shop, which has now closed down, said: "It's blocking passing trade, it doesn't look nice.
"Most of the time I see the people change their way. They cross the road, passing on the other side."
The substation, which is owned by ScottishPower, was moved from its original home inside the RAC building on the corner of Oswald Street and and Argyle Street, when it was demolished by developers Buccleuch Property.
Buccleuch was responsible for getting a permit from the council to place it somewhere until a new building was built to house it.
A spokesman for ScottishPower said the substation, which helps to manage the local electricity network, is an important piece of infrastructure.
The substation has now been situated in the middle of the pavement – blocking passing trade for shop owners – for the past three years.
Work on the Evolution building, which was set to replace the old RAC building, was due to start in January 2008.
But, Buccleuch say, the recent economic downturn has postponed these plans.
Kamran Ferooq, of IcareRepairs, in Oswald Street, says his business has only three months left if things don't improve.
He said: "Three months and I'm totally finished, nobody wants to come on this side of the street."
Huseyin Karaca, the owner of Expert Stitches tailors, moved into his store with the substation already outside and was given assurances that it would soon be moving.
He said: "They said it would be temporary, and that it wouldn't be long – I don't think more than one year, they said.
"But it's now more than three years."
John Brown, 50, who runs John Brown hairdressing, said he had no warning that the substation would be erected.
He said: "Right out the blue they came, put this shed down. I was asking them what it was all about.
"I thought it's going to be a wee thing, but then I realised it's going to be a big thing."
"I had done my salon up really nice and then they came along and took all the goodness of what I've done in the salon away.
"It's an eyesore. People look at that when they are walking down a street and will go the other way.
"If two or three clients do that to me every day, over three years it's a lot of business lost."
A spokesman from Buccleuch Property, said: "We've been working with the local authority and ScottishPower regarding our redevelopment proposals.
"We previously put them on hold because of the recession, but fortunately for all we are in a position now where we hope to be on site early next year with a major redevelopment on the site, which will incorporate the substation."
A ScottishPower spokesman said: "The substation was moved in to the street to facilitate a new development on Oswald Street.
"We have spoken to the developer and the City Council, and if the developer wishes to move the substation, we would be more than happy to discuss this with them."
A spokesman from Glasgow City Council said: "The location of power infrastructure is, ultimately, a matter for the company that owns it. Any application to move equipment could be considered through statutory planning processes."