Thousands attending the 20th annual Birthday Bash this month at the Waikiki Shell could be forced to celebrate alcohol-free.

Centerplate, the licensed city concessionaire at the Shell, faces a battle with prosecutors to renew its license before the Honolulu Liquor Commission on July 22.

If the commission decides to revoke the license because of problems the company has had enforcing drinking laws, Centerplate may not be allowed to sell liquor at the Shell, including for the KCCN FM 100 Birthday Bash, Hawaii’s largest two-day music festival.

Centerplate, which also sells liquor at the Neal Blaisdell Center and Aloha Stadium, rang up $435,700 in gross liquor sales, including taxes, at the Waikiki Shell in 2009.

Rick Schneider, chief executive officer of Events International, which produces the Birthday Bash, argued that even if Centerplate lost its license, it would be able to continue to sell alcohol during the appeals process. He said the Birthday Bash would go on even if the liquor license is not renewed.

Commission Chairman Dennis Enomoto said if Centerplate’s license is not renewed, it’s a possibility that Centerplate could not sell alcohol at the party.

"Everything is based on public safety," he said. "If we think there’s a public safety issue, we would get involved."

Schneider said Centerplate is getting a "raw deal" because the vendor already pays for security to spot underage drinking.

"They do a good job," he said. "It would be virtually impossible to do a better job."

This year’s Birthday Bash is scheduled for July 30 and 31 and features several local artists, including Kapena, Rebel Souljahz and Fiji.

At a hearing Tuesday attended by three of the commission’s five members, Centerplate officials from the mainland showed up to plead their case. But the panel delayed the hearing to July 22 so all five members could hear the case.

Centerplate officials declined to comment because the case is pending.

Sidney Quintal, director of the city Department of Enterprise Services, which oversees the Waikiki Shell, also declined to comment.

According to Liquor Commission documents, Centerplate doesn’t provide enough security personnel during events, which places an "unreasonable burden" on police and liquor enforcement officials.

The Birthday Bash, the documents added, has been a source of problems for years.

In 2007, the Honolulu Police Department told the commission that it assigned 50 to 60 officers to the park next to the Shell to prevent problems during the Birthday Bash.

In 2008, six minors were caught with liquor at the event. In 2009, liquor enforcement investigators caught seven minors drinking at the event.

During a hearing for citations issued at the 2008 Birthday Bash, Centerplate officials said they assigned three "spotters" to look for liquor violators, but removed them after dark because of the potential for violence.

Only 18 security officers were on scene for the more than 7,000 concertgoers on each of the two nights of the 2008 Birthday Bash, commission documents said.

In response, commissioners suggested the concessionaire set up beer gardens to create distinct, separate drinking areas. The commission also criticized the vendor for poor communication among security officers.

At a February hearing, the commission found the licensee had failed to take reasonable precautions when it assigned three spotters to monitor for liquor violations in a crowd of 3,000 concertgoers in October.

Then this spring, liquor investigators cited the licensee for four counts of allowing consumption by a minor and seven counts of possession of illegal drugs on the premises.