Maryland’s gambling expansion plan would allow Las Vegas-style table games. (AP Photo by Robert F. Bukaty)

With Penn’s latest contribution, total spending by companies with a stake in Question 7 now exceeds $24 million, more than the candidates spent in Maryland’s last governor’s race.

Penn in fighting the expansion plan, which would allow a new casino in Prince George’s County, as well as table games, such as black jack and roulette, at Maryland’s five previously authorized slots locations.

Companies that favor the plan have collectively ponied up more than $11 million, with much of that going to an escalating ad war on television, radio and the Internet.

One of those companies, Caesars Entertainment, is holding a news conference Tuesday afternoon to talk about its planned Harrah’s-brand casino in Baltimore, which company officials have said would be improved by the ability to offer table games.

A group led by Caesars has contributed about $2.3 million to the ballot campaign so far.

The biggest-spending proponent, MGM Resorts, has given $8.4 million. MGM is angling to build a casino at National Harbor in Prince George’s. The developer of National Harbor has chipped in $400,000.

Penn owns Rosecroft Raceway, a Prince George’s facility that would be eligible to bid for a casino license if the expansion plan passes. But Penn officials argue the deck is stacked against them, because Prince George’s County Executive Rushern L. Baker III (D) and others have championed National Harbor as a casino site.

Penn also owns a casino in Charles Town, W.Va., that analysts say would take a significant hit if another large-scale venue opens in Maryland.