There are allegations that Cleveland Cavs owner Dan Gilbert made improper campaign contributions in Detroit.
Union activist Robert Davis wants Michigan state regulators to revoke Gilbert's gaming license.
Davis claims Gilbert's company, Quicken Loans, made illegal contributions to Mike Duggan's Detroit mayoral campaign.
Rules in Michigan ban casino owners from making political donations. Gilbert owns Detroit's Greektown Casino.
Earlier week, Gilbert took back an $80,000 contribution to a super PAC called Turnaround Detroit.
Quicken Loans told our Scripps sister station WXYZ that the donations didn't violate any rules.
In a statement, Quicken Loans said: "There is no violation of any Michigan gaming law or regulation. The PAC in question is an independent legal entity. In addition, no person regulated by the Michigan Gaming Control Board (MGBC) has contributed to this PAC during calendar years 2011, 2012 or 2013. Likewise, no person regulated by the MGCB is an officer or director of the PAC."
In a separate statement, a spokesperson for the MGCB said: "The Michigan Gaming Control Board received a complaint at 0930 today alleging political contributions by a Quicken Loans PAC. The complaint is currently under investigation and we are unable to comment during the investigative process."
A complaint was filed by union activist Robert Davis with documents showing the Quicken Loans PAC was established 10 years ago before Gilbert had a financial interest in Greektown. And the Quicken Loans PAC made direct contributions to Detroit Mayoral Candidate Mike Duggan and Detroit City Council candidates.
Davis says the MGCB should conduct an investigation that could lead to the Greektown Casino license being revoked.
In a statement from Duggan's campaign, "This is just another frivolous complaint from Robert Davis. The Quicken PAC is a lawful PAC that has contributed to several candidates. We are confident that there is no problem with the legality of this donation."