Seattle's franchisees aren't buying the new minimum wage laws. So, they're taking the city to court.

This week, the International Franchise Association (IFA) and five franchisees filed a lawsuit in the U.S. District Court in Seattle, opposing the minimum wage act in its current form.

The city's new law raises minimum wage to $15 an hour. However, while most small businesses have seven years to adjust to the change, franchisees have only been granted three years to raise employees' pay.

Related: Dunkin' Donuts Franchisees Forced to Raise Coffee Prices

"To be clear, we are not seeking special treatment for franchisees; we only want equal treatment," wrote IFA President Stephen J. Caldeira in an open letter to Seattle's City Council. "Franchisees own the stores, not the chains -- and should not be unfairly defined as big businesses."

The lawsuit alleges that the minimum wage ordinance violates the Equal Protection Clause of the U.S. Constitution by discriminating against small businesses purely for their franchised status, grouping them alongside companies with over 500 employees. In addition to the IFA, the plaintiffs include franchisees from AlphaGraphics, BrightStar Care, Comfort Inn and Holiday Inn Express.

To spread the word on the lawsuit, the franchisees ran a full-page ad in the Seattle Times on Thursday. The ad includes Caldeira's open letter to the City Council, and reiterates franchisees' goal of equal treatment.

Related: Seattle Says Franchises Aren't Small Businesses, Forces Them on $15 Wage Fast Track