During the early 1950s, controversy arose regarding a supposed rivalry between Tebaldi and the great Greek-American soprano Maria Callas.
The contrast between Callas's often unconventional vocal qualities and Tebaldi's classically beautiful sound resurrected an argument as old as opera itself, namely, beauty of sound versus the expressive use of sound.

In 1951, Tebaldi and Maria Callas were jointly booked for a vocal recital in Rio de Janeiro, Brazil.
Although the singers agreed that neither would perform encores, Tebaldi took two, and Callas was reportedly incensed.

This incident began the rivalry, which reached a fever pitch in the mid-1950s, at times even engulfing the two women themselves, who were said by their more fanatical followers to have engaged in verbal barbs in each other's direction.
Tebaldi was quoted as saying, "I have one thing that Callas doesn't have: a heart" while Callas was quoted in Time magazine as saying that comparing her with Tebaldi was like "comparing Champagne with Cognac.
No, with Coca Cola."
However, witnesses to the interview stated that Callas only said "champagne with cognac", and it was a bystander who quipped, "No, with Coca-Cola", but the Time reporter attributed the latter comment to Callas.

According to John Ardoin, however, these two singers should never have been compared.
Tebaldi was trained by Carmen Melis, a noted verismo specialist, and she was rooted in the early 20th century Italian school of singing just as firmly as Callas was rooted in 19th century bel canto.
Callas was a dramatic soprano, whereas Tebaldi considered herself essentially a lyric soprano.
Callas and Tebaldi generally sang a different repertoire: in the early years of her career, Callas concentrated on the heavy dramatic soprano roles and later in her career on the bel canto repertoire, whereas Tebaldi concentrated on late Verdi and verismo roles, where her limited upper extension and her lack of a florid technique were not issues.
They shared a few roles, including Tosca in Puccini's opera and La Gioconda, which Tebaldi performed only late in her career.

The alleged rivalry aside, Callas made remarks appreciative of Tebaldi, and vice versa.
During an interview with Norman Ross in Chicago, Callas said, "I admire Tebaldi's tone; it's beautiful – also some beautiful phrasing.
Sometimes, I actually wish I had her voice."
Francis Robinson of the Met wrote of an incident in which Tebaldi asked him to recommend a recording of La Gioconda in order to help her learn the role.
Being fully aware of the alleged rivalry, he recommended Zinka Milanov's version.
A few days later, he went to visit Tebaldi, only to find her sitting by the speakers, listening intently to Callas's recording.
She then looked up at him and asked, "Why didn't you tell me Maria's was the best?"
According to Time magazine, when Callas quit La Scala, "Tebaldi made a surprising maneuver: she announced that she would not sing at La Scala without Callas. '
I sing only for artistic reasons; it is not my custom to sing against anybody', she said."

Callas visited Tebaldi after a performance of Adriana Lecouvreur at the Met in 1968, and the two were reunited.
In 1978, Tebaldi spoke warmly of her late colleague and summarized this rivalry:
This rivality [sic] was really building from the people of the newspapers and the fans.
But I think it was very good for both of us, because the publicity was so big and it created a very big interest about me and Maria and was very good in the end.
But I don't know why they put this kind of rivality [sic], because the voice was very different.
She was really something unusual.
And I remember that I was very young artist too, and I stayed near the radio every time that I know that there was something on radio by Maria.
During the early 1950s, controversy arose regarding a supposed rivalry between Tebaldi and the great Greek-American soprano Maria Callas. The contrast between Callas's often unconventional vocal qualities and Tebaldi's classically beautiful sound resurrected an argument as old as opera itself, namely, beauty of sound versus the expressive use of sound.
In 1951, Tebaldi and Maria Callas were jointly booked for a vocal recital in Rio de Janeiro, Brazil. Although the singers agreed that neither would perform encores, Tebaldi took two, and Callas was reportedly incensed. 
This incident began the rivalry, which reached a fever pitch in the mid-1950s, at times even engulfing the two women themselves, who were said by their more fanatical followers to have engaged in verbal barbs in each other's direction. Tebaldi was quoted as saying, "I have one thing that Callas doesn't have: a heart" while Callas was quoted in Time magazine as saying that comparing her with Tebaldi was like "comparing Champagne with Cognac. No, with Coca Cola." However, witnesses to the interview stated that Callas only said "champagne with cognac", and it was a bystander who quipped, "No, with Coca-Cola", but the Time reporter attributed the latter comment to Callas.
According to John Ardoin, however, these two singers should never have been compared. Tebaldi was trained by Carmen Melis, a noted verismo specialist, and she was rooted in the early 20th century Italian school of singing just as firmly as Callas was rooted in 19th century bel canto. Callas was a dramatic soprano, whereas Tebaldi considered herself essentially a lyric soprano. Callas and Tebaldi generally sang a different repertoire: in the early years of her career, Callas concentrated on the heavy dramatic soprano roles and later in her career on the bel canto repertoire, whereas Tebaldi concentrated on late Verdi and verismo roles, where her limited upper extension and her lack of a florid technique were not issues. They shared a few roles, including Tosca in Puccini's opera and La Gioconda, which Tebaldi performed only late in her career.
The alleged rivalry aside, Callas made remarks appreciative of Tebaldi, and vice versa. During an interview with Norman Ross in Chicago, Callas said, "I admire Tebaldi's tone; it's beautiful – also some beautiful phrasing. Sometimes, I actually wish I had her voice." Francis Robinson of the Met wrote of an incident in which Tebaldi asked him to recommend a recording of La Gioconda in order to help her learn the role. Being fully aware of the alleged rivalry, he recommended Zinka Milanov's version. A few days later, he went to visit Tebaldi, only to find her sitting by the speakers, listening intently to Callas's recording. She then looked up at him and asked, "Why didn't you tell me Maria's was the best?" According to Time magazine, when Callas quit La Scala, "Tebaldi made a surprising maneuver: she announced that she would not sing at La Scala without Callas. 'I sing only for artistic reasons; it is not my custom to sing against anybody', she said."
Callas visited Tebaldi after a performance of Adriana Lecouvreur at the Met in 1968, and the two were reunited. In 1978, Tebaldi spoke warmly of her late colleague and summarized this rivalry:
This rivality [sic] was really building from the people of the newspapers and the fans. But I think it was very good for both of us, because the publicity was so big and it created a very big interest about me and Maria and was very good in the end. But I don't know why they put this kind of rivality [sic], because the voice was very different. She was really something unusual. And I remember that I was very young artist too, and I stayed near the radio every time that I know that there was something on radio by Maria.
Renata Tebaldi