Burger chain White Castle is conducting an agency review, the company confirmed Friday.

The incumbent, Omnicom's Zimmerman, has led the fast-food brand's creative and media efforts since 2009. Prior to that, JWT spent 15 years as White Castle's agency of record.

"We always look at all of our partners on a regular basis, every five to seven years," said Kim Bartley, White Castle VP-marketing and menu development. The marketer issued a request for proposals to agencies in June and has seven shops in the running, she said. It plans to make a decision by October.

"Zimmerman is one of the agencies being considered," she added. "It's a very good partner."

Zimmerman called the review normal procedure for White Castle. "We're very proud of the work our companies have done together," a Zimmerman spokesman said in a statement, "and we're happy to go in and present additional work, confident that our successful partnership will continue."

White Castle spent more than $9 million in measured media in 2013, according to Kantar Media. The company has no plans to increase its ad spend in the short term, according to Ms. Bartley. "But we're long-range planners," she said. "This year, we are 93 years old."

The review comes five months after Zimmerman lost the much larger Papa John's business to Grey.

Part of the criteria will be plans to broaden White Castle's appeal and contemporize the brand, Ms. Barley said. "It's about showing business acumen, combining traditional and digital," she said.

Rojek Consulting Group is assisting the effort, the third White Castle review for Rojek President Lorraine Lockhart. "What used to be a more operationally-driven company is now more marketing and brand driven," Ms. Lockhart said.