Shares dropped as low as 40 percent during the day.
CEO Alvin Chau is the subject of an arrest warrant in mainland China, where gambling is illegal.
He and others have also been accused of money laundering.
They allegedly engaged in this by using the world's largest gambling hub to run an illegal "live web betting platform" in the Philippines that attracted mainland Chinese.
Some experts suggest this signals a new era for gambling in Macau with Beijing no longer tolerating any promotion of the activity on the mainland.
News of the arrests already spooked investors on Monday, sending down shares of major casinos in the city.
As Suncity Group takes stock of recent developments, it says Chau intends to resign from his position.
And in a statement released on Monday, it added that operations would not be impacted in the event that it ceased to have his support.
