The political squabbling over the collapse of Philadelphia’s coronavirus vaccine partnership is getting hotter.

City Councilmember Cindy Bass took the unusual step Monday of asking Mayor Jim Kenney himself to testify about the administration’s now severed partnership with the group Philly Fighting COVID. Kenney declined to appear at the Friday hearing, his office confirmed Tuesday. Several members of his administration will testify, including chief of staff Jim Engler, Managing Director Tumar Alexander, and Health Commissioner Thomas Farley.

But Bass said Tuesday that Kenney himself needs to answer for the implosion of the city’s partnership with the group, which slowed vaccination progress in Philadelphia and garnered embarrassing national headlines.

“At the top of the food chain, he is the responsible party for contracts, whether they be written, verbal, a handshake agreement, a wink and a nod — the buck stops with the mayor,” Bass said in an interview. “I feel strongly that he should step up and have these conversations with the citizens of Philadelphia.”

Kenney’s declining Bass’ invitation is neither surprising nor without precedent. But it speaks to the level of antagonism the Philly Fighting COVID debacle has sparked between the administration and City Council, and suggests more tension to come at Friday’s hearing.

Kenney wrote in a letter to Bass on Tuesday that he has “no unique knowledge that could assist City Council in its investigation.”

The only time mayors typically appear before Council is for the annual budget address. When lawmakers hold oversight hearings on administration actions, they usually interrogate department heads, the managing director, or members of the mayor’s staff.

“I cannot recall a time that a sitting mayor has been subjected to questioning by a City Council committee investigating an issue,” he wrote. “I share your frustration and disappointment regarding Philly Fighting Covid, and like you want to ensure all questions are answered in an expeditious manner. Philadelphians’ lives are at stake and we need to rebuild that trust immediately.”

» READ MORE: The city trusted a group of ‘college kids’ to lead its vaccine rollout. But Philly Fighting COVID was full of red flags from the start.

Council’s public health and human services committee, which Bass chairs and will hold Friday’s hearing, also took about 10 minutes of testimony in November from Philly Fighting COVID CEO Andrei Doroshin and failed to question his credentials. Members of the committee attended the opening of the group’s vaccination clinic at the Convention Center. But since the city cut ties with the organization last week, lawmakers have emphasized that they don’t oversee contracts and have sharply criticized the Kenney administration.

Doroshin, 22, confessed last week to taking several vaccine doses from the Convention Center to administer to his girlfriend and friends. At a combative news conference Friday, he called for Farley’s dismissal.

Deputy Health Commissioner Caroline Johnson resigned Saturday after records obtained by The Inquirer showed she gave PFC an advantage in a city bidding process. Bass and City Council President Darrell L. Clarke introduced legislation on Monday that would allow for more oversight of the city’s vaccine rollout, including the process for awarding contracts.

The city’s Office of the Inspector General is conducting an investigation into the relationship between the health department and PFC, as the department attempts to regain public trust and ramp up vaccine distribution. Farley said Tuesday that the city, one of only a handful nationwide to be given vaccines directly by the federal government rather than through the state, will open its own mass vaccination clinics by the end of the month.

But outraged constituents are reaching out to lawmakers in the meantime, demanding answers — and vaccines. “Council is supposed to exercise a check and balance on the administration, and it should be doing that during this emergency,” Councilmember David Oh said in an interview Tuesday.

» READ MORE: Philly Fighting COVID’s founder met with City Council about vaccines in November. No one asked about his credentials.

Kenney said at a news conference Tuesday that he understands he is “blamed for most things” because he’s the mayor.

“That comes with the territory,” he said. “I’ve got my big boy pants on.”

The health department ended its relationship with PFC after The Inquirer questioned the city about the group’s privacy policy, which allowed it to sell personal data through a previously undisclosed for-profit arm.

Many Philadelphians who saw the grand opening of Philly Fighting COVID’s mass vaccination site at the Convention Center thought it was city-sponsored. The official city seal was plastered around the clinic and officials in attendance at the launch included Kenney and Bass.

Bass, a frequent Kenney critic who is widely seen as a potential candidate for mayor in 2023, has blamed her attendance at the event on the Kenney administration.

“At no time in any way, shape, or form … was I ever told or informed that this was an outside entity, that we had a verbal contract with, that was doing these vaccinations with no experience,” Bass said during a news conference Tuesday. “These things all came to light afterward.”

Several lawmakers joined in criticism of the administration last week, echoing Bass’ demand for answers.

”You know I hold both of you in high esteem … but I want to know who made the call?” Councilmember Cherelle Parker, a Kenney ally, said in comments directed toward Kenney and Farley during a Council meeting last week. “I want to know who put their credibility on the line. I want to know who said, ‘This is a green light.’ ...?”

“We have to make sure that the confidence of the citizens of the city of Philadelphia is in place, and it’s not there now. I’m getting calls from all over about what the heck’s going on,” Clarke said at a news conference Monday. “The city of Philadelphia is basically an embarrassment across the country.”

Councilmember Bobby Henon, meanwhile, has defended the group. His office acknowledged Friday that Philly Fighting COVID provided at-home coronavirus tests for his family. Henon is vice chair of the public health and human services committee.Those tests were first reported by WHYY.

Kenney and Farley sought to reassure residents Tuesday.

“I can understand everybody’s on edge, everybody’s stressed out,” Kenney said. “A lot of the stress has to do with the fact that we have very little vaccine. So I understand people’s consternation.”

Staff writer Sean Collins Walsh contributed to this report.