CHICAGO (CBS) — The Cubs have won approval from a landmark review panel for a new advertising sign in the Wrigley Field bleachers, but they could face a big hurdle ahead.

A permit review committee of the Commission on Chicago Landmarks gave preliminary approval to the Cubs’ plan. But the Chicago Sun-Times’ David Roeder reported the vote was divided at 3-2, over concerns that the small-scale changes the Cubs are making to Wrigley Field could ultimately result a major difference in the structure.

Ald. Tom Tunney (44th), whose ward includes Wrigley Field, said he will back an ordinance to get full City Council approval before making any changes to the ballpark.

Tunney wants to set ground rules for any more ads that might go up at the ballpark. Roeder reports those ads would apply to any electronic sign of at least 100 square feet, Roeder reported.

Tunney has given preliminary approval to the sign the Cubs are planning now, the Cubs reported.

The planned sign would be mounted near the right field corner in the Bud Light Bleachers, and would feature game information. A patio and seating area behind the sign would replace rows of bleachers that have already been taken out, Roeder reported.

The change means the seating capacity in that section of the ballpark has been reduced from 252 to 156, but the Cubs hope to make up the difference by getting premium prices for group access to what Roeder characterizes as an “in park rooftop experience.”

The Cubs want the sign in place by opening day on April 5.

For many years, there was no large-scale advertising inside Wrigley Field.

Instead, advertising was instead placed on buildings surrounding the ballpark. The advertising includes a sign wrapped over the sloping rooftop of the building at Waveland and Kenmore avenues, which has advertised Budweiser beer, Horseshoe Casino, and most recently United Airlines. Also, the graystone building at 3631 N. Sheffield Ave. is known for its billboard advertising Torco oil, and more recently Miller Lite beer.

But two years ago, a sign advertising Toyota was mounted on two steel poles above the left field bleachers. The sign was wildly unpopular with many fans when it up.

Other ads have popped up within the ballpark since then, Roeder reported.