Parker held a news conference on Wednesday morning to confirm that her previously announced deadline has not changed.
She made it clear she was not backing down.
"I am at war... with the status quo here in the city of Philadelphia," she said.
Her announcement came just days before that deadline, and about a week after a lawsuit was filed by a union representing thousands of city workers.
"I believe that the workplace allows for personal and productive interactions for facilitating communication, promoting social connections, along with collaboration, innovation, inclusion and belonging," Parker said.
About 80% of the city's 26,000 employees have been working fully on-site since last year. The rest have been on a hybrid schedule.
The lawsuit, filed by AFSCME District Council 47, claims the elimination of remote work would "cause substantial harm for city workers and will throw services into chaos."
Brett Bessler, vice president and business agent for DC 47, says the decision also makes it tempting for those union workers to leave.
"Montgomery County tweeted out 'Come work for us, we offer hybrid work.' The counties are already poaching our best and brightest. They are going to continue to do so," he said.
The mayor sees this not only as a policy that expired with the COVID-19 pandemic emergency but also as a larger economic issue.
"We also want to set a standard for how the city economy and other corporate, nonprofit, and other government entities return to the office in an effort to make a more vibrant Philadelphia. That's the ultimate goal," she said.
Parker specifically thanked workers from various city agencies including police officers, firefighters, correctional officers, sanitation workers and more.
"These individuals have never had the ability to change the location of their work during a global pandemic, and made great personal sacrifices for the city," she said Wednesday.
Mayor Parker news conference reaffirming return to office date for Philadelphia city workers
The mayor announced the mandate in May, saying she wanted to create a more visible and accessible government.
Union presidents of Local 2186 and 2187 posted an explanation on Facebook after the lawsuit was filed.
"We are placing this decision in the hands of a judge and asking that no one be returned to the office until this disagreement is processed through the proper channels, highlighted in our contracts," said David Wilson with AFSCME District Council 47 and Local 2187.
Villanova Law Professor Ann Juliano says, in the end, the lawsuit will win or lose on one legal point: whether this decision falls under the collective bargaining agreement the city made with the unions.
"Their argument might be, 'We don't have to bargain over this because this was never a formal condition of work,'" Juliano said. "If the judge says this is a condition of work that has to be collectively bargained, then the city violated that provision."
Parker has said her administration does not believe the return to office policy is subject to collective bargaining.