Illinois Gov. Pat Quinn on Tuesday rejected a bill to expand gambling in the state, including a new land-based casino in Chicago, saying the proposal lacked sufficient regulatory oversight.

With two of his predecessors in prison, the Chicago Democrat has made it clear he must preserve his political integrity in the plan, which also proposed establishing four new riverboat casinos and allowing slot machines at racetracks.

The most glaring omission from the bill "is the absence of strict ethical standards and comprehensive regulatory oversight. Illinois should never settle for a gaming bill that includes loopholes for mobsters," Quinn said in a prepared statement.

Supporters of the bill estimated the expansion could have brought in up to $1 billion a year, boost tourism and create 100,000 jobs for the state.

Chicago Mayor Rahm Emanuel supported the establishment of a city casino.

But opponents said more casinos could saturate some markets and raised concerns about the social cost.

The proposal would have established a city-owned Chicago casino with spots for 4,000 people to gamble at once. It also would have added riverboat casinos in Danville, Park City, Rockford and an undecided location in Chicago's south suburbs. Each riverboat casino would have had 1,600 gambling positions, and allowed Illinois' 10 existing casinos to grow.

Expanded gambling in Illinois could put a further hit on Indiana's 20-year-old casino industry, which saw admissions fall to their lowest level in 14 years in 2011.

Earlier attempts at expanding gambling in Illinois have failed. Lawmakers approved a similar plan last year but did not send the plan to the governor, who had threatened a veto.

Quinn, who isn't opposed to gambling on principal, had said all along that he wanted a bill with stronger ethical protections. That includes barring the gambling industry from making political contributions.

"Everybody should be concerned about ethics in our state. We have two governors, my predecessors, both in jail. That's a pretty darn important issue for our state to have integrity at all times in every part of government, and that includes regulating casinos," he said Monday. "It must be airtight when it comes to protecting the public."

In response, lawmakers also filed a so-called trailer bill to address some of Quinn's concerns. However that wouldn't be considered unless the initial law is signed, and Quinn has said he'd rather get all the legislation signed at once.