A Lansing-based campaign watch-dog group believes Tony Benavides violated state campaign finance laws.
The Michigan Campaign Finance Network says Benavides has not paid rent on his campaign headquarters on E. Michigan Avenue.
The owner of the property gave Benavides the space for six months as a $600 donation.
Michigan election law limits donations to mayoral candidates to $1,000.
The MCFN chairman says the offices are usually leased for $1,200 a month.
Benavides' opponent Virg Bernero wants the mayor to pay back what any illegal campaign contributions.