Rep. Robert Brady (D., Pa.) has also weighed in, with a letter to Nutter in support of the coalition.
"I am asking the city to rethink its current renovation plans, while taking into consideration the national historic importance of the property," Brady wrote.
A spokesman for the city confirmed that "at this point, everything is suspended in terms of renovation work pending further discussions."
The coalition also wants a complete engineering study of the playground, at Queen and Lawrence Streets, before proceeding with any kind of construction. The ground is marked by a sinkhole and depressions, and the property is bordered by a 180-year-old water main along Queen.
The burial ground was designated a local landmark last year by the Philadelphia Historical Commission.
Joe Certaine, managing director in the Rendell administration, said Gillison told his group, the Friends of Bethel Burial Ground Coalition, that the playground renovation project is "now being monitored through the mayor's office."
In a statement conveyed through the city spokesman, Mark McDonald, Gillison said: "We will take whatever measures are needed to ensure a positive resolution and way forward."
Certaine and others in his group have been concerned that the city has largely ceded decision-making regarding its own property to outside groups, in this case Mother Bethel A.M.E. Church and the Queen Village Neighbors Association. They also expressed concern that city decisions regarding a nationally significant historic site have been relegated to lower-level department heads, in this case the head of Parks and Recreation.
"The mayor's office works with its line departments on issues, so there's no 'takeover' here," McDonald said in an e-mail. "We are working with all parties that have expressed interest in this matter."
The burial ground, which holds the remains of more than 5,000 people buried between 1810 and the mid-1860s, has been owned by the city since the 1890s. More than 2,100 of those interred there have been identified by independent historian Terry Buckalew, whose work is publicly available at preciousdust.blogspot.com.
A public meeting to discuss the site - its historical significance, contemporary threats, and potential commemoration - will be held at 10 a.m. Saturday at the African American Museum of Philadelphia, Seventh and Arch Streets.
Gillison said he wanted to hold a meeting next week to bring together interested parties to discuss the situation, according to Certaine. McDonald said he had no information on when a meeting might occur.
The playground, owned by the city, has been managed by the Department of Parks and Recreation. Rosalyn J. McPherson, president of the Roz Group, a strategic planning and communications firm, said she had been asked "by the city and Mother Bethel and Parks and Recreation" to "do planning, potential planning," for commemoration of the burial site.
In a Feb. 14 e-mail, McPherson called for suggestions for "names of artists or sculptors who can envision a broad range of possibilities including mural, bench, sculpture, etc. for the site."
On Thursday, she said "nothing definitive" had been done. "It's all about what could be done," she added.