Prime Minister Lee Hsien Loong has condemned the racist remarks made by former NTUC assistant director Amy Cheong on Monday.
Writing on his Facebook page, Mr Lee said he was "shocked to hear about this."
"The comments were just wrong and totally unacceptable," he said.
He said that while Ms Cheong has promptly apologised for her grievous mistake, the damage had been done.
"NTUC did the right thing in terminating her services," he added.
He called on Singaporeans to treat the incident as "an isolated case that does not reflect the strength of race relations in Singapore".
He added: "But it sharply reminds us how easily a few thoughtless words can cause grave offence to many, and undermine our racial and religious harmony.
"Let us all be more mindful of what we say, online and in person, and always uphold the mutual respect and sensitivity that holds our society together," he wrote.
Separately, three ministers and an MP have also weighed in, criticising the racists remarks and praising the Labour Movement for their quick action against her.
NTUC fired Ms Cheong earlier on Monday, hours after the furore began.
Deputy Prime Minister Tharman Shanmugaratnam said in a post: "Good that NTUC acted quickly. The person's comments were offensive not only to Malay-Muslims, but all the rest of us who value Singapore's multiracial spirit and who want to take it further."
Similarly, Law Minister K. Shanmugam, said Ms Cheong's comments and conduct were "shameful and completely unacceptable."
"Her comments reflect a deep seated racist attitude coupled with contempt for those who are less well off, or who wish to spend less," he wrote.
He also said that Ms Cheong's behaviour confirms what he had long suspected to be deep fault line - based on race or religion - in Singapore's society.
He added: "I am glad that NTUC took swift action to terminate her employment. This should send a message that such conduct will not be tolerated."
Earlier on Monday, Acting Manpower Minister, Tan Chuan-Jin wrote that give and take was part of life here: "We all give and take. Most live and let live. Many are proud of this colourful tapestry that we have here. This is part of what it means to be Singaporean."
Pasir Ris-Punggol GRC MP Janil Puthucheary took the opportunity to talk about diversity. He said celebrating diversity meant more than just tolerating the neighbours or understanding other cultures.
He wrote: "It means seeing the differences amongst us as a source of happiness, wonder and joy. It means feeling the sparkle and passion that variety gives to our lives.
"It means seeking a connection at a fundamental level that connects us as humans and yet being open to the possibility of learning more, moving closer, journeying together."