The banner, in West Bromwich Albion colours, can be seen by thousands of motorists travelling past each day.
But Sandwell Council has asked for it to be removed – with bosses accused of threatening Mr Galloway with prosecution and using “mafioso tactics” to scupper his election campaign - something the authority has denied.
The 65-year-old is fighting against the removal of the 42-feet wide banner and has vowed to take the council to court over the matter.
Mr Galloway was kicked out of Labour in 2003 for comments on the Iraq war.
He is standing as independent pro-Brexit candidate in West Bromwich East.
His banner is hanging from the old Grade ll-listed Kenrick House building in the town.
The Labour-run council said it was not seeking to take action against Mr Galloway but had stepped in as banners are not allowed to be hung from listed buildings.
But Mr Galloway believes the move is part of a political campaign against him by Labour politicians in Sandwell.
He also claims the council has pressured pubs and schools into stopping him from using them as venues for public meetings and hustings.
He said: “They want to prosecute me for putting it up.
“I have come to West Bromwich to stand up against the Labour-run council, and they have threatened me with prosecution for putting up the banner – which will be taken down on December 13.
"The owner of the platform gave me permission to put up the biggest banner in the country.
“I have never been in an election quite like this.
"It is a series of things all of which add up to determination on the part of Sandwell Council to cripple my election campaign.”
When he first emerged as a candidate, Mr Galloway claimed that one of his first priorities if elected would be to investigate allegations of corruption in the council.
He has questioned why no official hustings have taken place, accusing Labour and the Tories of colluding to ensure there were no such head-to-head debates ahead of polling day.
He says schools have failed to make their premises available to him – despite being required to do so by law during elections – and that pubs have pulled out on hosting his public meetings.
“It is Labour, in one form or another, that is stopping the pubs from allowing us to use those premises and has let it be known to schools,” he claimed.
He said that three pubs had cancelled appearances from him, with one saying they had been put under “pressure”.
“This is mafioso tactics,” Mr Galloway said.
“It is Sandwell Council that licenses them. It is the Sandwell Council department that they need to satisfy.
"This is not democratic. I am supposed to trust this council to run the election fairly.”
A Sandwell Council spokeswoman said: “We have contacted all of our schools to remind them of their obligation to provide facilities for candidates in the General Election to hold public meetings. However, given the time of the year, one of the three schools involved had a pre-planned event and could not accommodate the proposed meeting. We have asked Mr Galloway’s team for details of the other two schools so we can raise the matter with them.”
The spokeswoman added: “It is not an electoral offence to display election materials on private buildings provided the owner of the property has given permission.
“However, erecting a banner or making any changes to a listed building without consent from the council is not allowed, so we have asked the owner of the building to remove it .”
The spokesman said the council would be contacting schools to raise the issue of providing facilities for candidates.
Mr Galloway’s opponents include Ibrahim Dogus for Labour and Nicola Richards for the Conservatives.
Tom Watson is standing down.
Plans have been lodged to revamp the former headquarters of manufacturer Archibald Kenrick & Sons into flats, office space and storage.