Burger King recently sent out a letter to its largest competitor, McDonald’s. This letter was an invitation to join burger forces in the name of peace. The goal was to come together and create the McWhopper, a hybrid burger that would be created, and sold for one day only at a pop up stand in Atlanta. The goal was to promote the message of peace while raising money for the peace foundation. Sadly McDonald’s has declined the peace day offer, saying they believe their company’s can do something greater for peace.

Late Tuesday, Burger King issued a new letter announcing it will work with a few chains on its pop-up Peace Day shop, including some much smaller players that could see their popularity rise, thanks to the publicity. The plan now includes Denny’s, Krystal, Wayback Burgers and Giraffas.

Krystal issued its own playful letter when it joined the conversation on Aug. 26, the same day Burger King issued its public offer to McDonald’s.

Burger King says that it wants to combine one key ingredient from each restaurants’ signature sandwich to create one Peace Day burger. The pop-up restaurant is already under construction, so the chains simply have to confirm their interest and make a donation to Peace One Day.

“The ‘Peace Day Burger’ is the ultimate collaboration from some of the best burger forces in America and, as America’s Diner, it is only fitting that Denny’s help lead the way with this unique burger merger.”

In 2001, International Peace Day was created by the United Nations General Assembly to promote nonviolence and a cease-fire. The theme of this year is “Partnerships for Peace—Dignity for All,” which is aimed at promoting nations and people working together for the common good.