"I cannot accept this way of doing things," Cardinal Gerhard Muller said in an interview with German newspaper Passauer Neue Presse.
Francis informed Muller, the former head of the Congregation for the Doctrine of the Faith, Vatican's doctrinal office, that he would not be renewing his contract
in a brief meeting on June 30, just two days before the contract expired.
"He did not give a reason," the 69-year-old cardinal said in the interview. "Just as he gave no reason for dismissing three highly competent members of the CDF a few months earlier."
Greg Burke, director of the Vatican Press Office, told CNN: "It was a private meeting with the Pope. We have no comment."
Muller's ouster came during a tumultuous week for the Vatican. On June 29, Australian police announced four sexual assault charges against Cardinal George Pell, the head of the Vatican's secretariat for the economy and a top adviser to Pope Francis. Pell has returned to Australia to face the charges.
Muller is not just another disgruntled employee. Although he has been removed as a Vatican official, he remains a cardinal of the Catholic Church, which makes his public criticism of the Pope even more striking.
"I have said this before -- the church's social teaching must also be applied to the way employees are treated here in the Vatican," Muller said, implying that there has been a disconnect between the Pope's teaching and how they are applied within his own curia.
Vatican employees have long complained that the church's lofty rhetoric about social justice and workers' rights aren't always respected inside the Vatican itself, said CNN's Vatican analyst, John Allen of Crux.
"What's unusual here is that the criticism isn't coming from a low-level employee in the Vatican Museums," Allen said, "but a Cardinal who has become a public symbol of tensions around Pope Francis."
Some of those tensions have to do with Francis' attempt to loosen up church doctrine, for example in the area of giving Holy Communion to divorced and remarried Catholics, an issue which has divided liberals and conservatives in the Catholic Church.
Muller, a conservative, was often seen to be in a difficult position as head of the Vatican's doctrinal office, between supporting the Pope's changes and reconciling them with the doctrinal rules.
"Although he is conservative, Muller never openly criticized the Pope for doctrinal matters," commented Vatican expert Andrea Gagliarducci of Catholic News Agency. "The issue is the way in which he was dismissed," he said.
"People forget," Gagliarducci added, "that there were many cardinals criticizing Benedict XVI and John Paul II at the beginning of their pontificates. No Pope pleases everyone."
Muller was replaced by Monsignor Luis Francisco Ladaria Ferrer, a Jesuit and current second in command for the Vatican's doctrinal watchdog.
Muller, 69, a German, was appointed by Francis' predecessor, Pope Benedict XVI, who himself once headed the Congregation for the Doctrine of the Faith.
A conservative, Muller was widely seen to be resistant to Francis' attempt to open up the church's teaching, particularly on the issue of allowing communion for divorced and remarried Catholics.
Unusually, Muller gave a recent interview in which he said there should not be different interpretations of church teaching on the subject, putting him at odds with Francis' thinking. The issue is one that divides liberals and conservatives in the church.
The Congregation for the Doctrine of the Faith is also in charge of handling sex abuse cases involving the church.
Francis promised to tackle the crisis, but has faced questions about a perceived lack of action.