Nationalists said they were "delighted" to have won the support of the uncle of Labour's new Scottish deputy leader.
Businessman Mohammad Ramzan, brother of former Glasgow Labour MP Mohammad Sarwar and the uncle of deputy leader Anas Sarwar, is reported to have said he would be backing the SNP in next week's council elections.
His comments come just days before the May 3 poll, with both Labour and the Nationalists fighting to win control of Glasgow City Council.
Mr Ramzan, the chairman of United Wholesale Grocers, told the Herald newspaper he would be supporting First Minister Alex Salmond's party in the local government elections.
He hit out at the current Labour administration in the city, saying: "I have been a businessman in Glasgow for over 35 years and I have always wanted what is best for the city.
"Unfortunately, under the current Labour administration the city has not moved forward, there is a lack of ideas and innovation, and they now spend more time squabbling among themselves than trying to help ordinary Glaswegians.
"That is why I will be supporting real change under the SNP."
SNP deputy leader Nicola Sturgeon said: "This is another sign of the growing support for the SNP in Glasgow and shows that the wind of change is blowing through the city."
Allison Hunter, the SNP group leader in Glasgow City Council, said: "I am delighted that Mr Ramzan is to support the SNP at the election next week. For a prominent businessman to endorse us in this way is hugely significant."