Hotel industry leaders received a green light Monday from the Denver City Council to initiate a new kind of tourism tax that would help pay for a rooftop expansion on the Colorado Convention Center.

Mayor Michael Hancock’s administration has made the hotel tax idea a key part of its multi-pronged plan to cover cost gaps in the now-$233 million project. In a 12-0 block vote, the council approved the ability to create a Tourism Improvement District — and now it’s up to hotel owners to initiate one that officials say will result in an additional 1 percent surcharge on stays at hotels with at least 50 rooms within Denver city limits.

“What comes next is that a petition will be drafted and signed by a minimum of 30 percent of the hotels” of that size, said Amie Mayhew, president and CEO of the Colorado Hotel and Lodging Association, which backs the initiative. “We anticipate that to happen before the middle of July.”

After that threshold is met, a series of steps would result in a special election Nov. 7 for 108 qualifying lodger’s tax license-holders. Together, they own 116 midsize and large hotels, including some with joint tax license accounts.

If a majority approve, the new surcharge would make the effective check-out tax paid by guests of those hotels 15.75 percent.

The city’s convention center project calls for an 80,000-square-foot ballroom and a 50,000-square-foot outdoor terrace with mountain and downtown views, built atop the existing parking garage. The project also includes technology upgrades and renovations of three downstairs lobbies.

Denver voters approved extensions for existing lodger’s and car rental taxes in 2015, and those are expected to provide $104 million for the project.

But the finalizing of the project’s scope and multiple building-related factors have driven the price much higher than that, spurring the hotel surcharge idea and other plans to tap city income related to the convention center.