Illegal pull-tab games are costing the Wisconsin Lottery millions in revenue but an audit says prosecutors have been reluctant to charge their operators.

An audit released Thursday found the Lottery's sales of pull-tab tickets fell to a low of $3.2 million in the budget year that ended June 30. Twenty years ago, they brought in $25 million a year.

The Lottery says competition from pull-tab games operating illegally at gas stations and taverns or under a loophole in state law accounts for the decline. Revenue Secretary Roger Ervin says a study found they cost the Lottery up to $23 million per year.

The audit says local prosecutors are reluctant to charge operators of illegal games, and the Department of Justice has investigated fewer cases in recent years.