MGM Resorts has opened an office at National Harbor, where it would like to build a casino. (Jeffrey MacMillan/ For The Washington Post)

Companies with a stake in Maryland’s ballot measure on expanded gambling have now shelled out more than $65 million for dueling campaigns, according to the latest disclosure reports.

MGM Resorts, the company angling to build a casino at National Harbor, has contributed another $8 million in recent days to a ballot-issue committee supporting Question 7. That brings MGM’s total outlay to $29.4 million.

The Peterson Cos., the developer of National Harbor, has also bumped up its contributions to the campaign to nearly $1.7 million, while a group that includes Caesars Entertainment has given $4.6 million.

Question 7 would allow a new Las Vegas-style casino in Prince George’s County, as well as table games, such as blackjack and roulette, at Maryland’s five previously authorized slots sites. The campaign is playing out through ads on television, radio and the Web.

The sole large funder of the opposition is Penn National Gaming, which has given $29.1 million to a ballot-issue committee called Get the Facts — Vote No on 7.

Penn’s properties include a casino in Charles Town, W.Va., that analysts say would take a hit if another large-scale venue opens in Maryland.

Besides its contributions to the main ballot committee supporting Question 7, called For Maryland Jobs and Schools, Peterson has given $500,000 to another pro-expansion committee led by former Prince George’s County Executive Wayne K. Curry (D).

A Washington Post poll released last week showed Maryland voters sharply split on Question 7.