Penny Mordaunt has torn into the SNP's Westminster Leader Stephen Flynn for not singing the National Anthem at the Cenotaph on Remembrance Sunday.
She demanded he do his "duty" and "show respect".
Speaking in the Commons, she said: "I'm sure Mr Speaker would take a dim view if I refused to answer the Honorable Lady's question.
"If I just stood here in silence because I didn't fancy doing it or I objected strongly to the content and tone of it.
Penny Mordaunt has torn into the SNP's Westminster Leader Stephen Flynn for not singing the National Anthem at the Cenotaph on Remembrance Sunday
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"He might ask if I had done that why I would have shown up this morning if I was not prepared to do my duty in this House, if I was not prepared to show respect to this House.
"It would be a bit like attending the Cenotaph and not singing the national anthem."
Writing on X, she added: "Today I advised the SNP: Respect others. Do your duty.
"And if you’ve turned up, join in the National Anthem."
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This came after Flynn was seen standing in silence during the National Anthem last weekend.
Scottish Conservative deputy leader Meghan Gallagher claimed the SNP's Westminster leader had "fallen shamefully short".
She said: "Stephen Flynn is entitled to his republican views, but as Westminster leader of the SNP he has a duty to show respect to our head of state and to all nations and anthems.
"By apparently refusing to join in with the national anthem, especially at a service to honour those who gave their lives for this country, he has fallen shamefully short of this."
But when these comments were put to the SNP, a source hit back, saying: "Pretty grotesque that the Tories are trying to politicise Remembrance Sunday".
Refusing to deny claims he wasn't singing, a spokesperson added: "Stephen Flynn was honoured to represent the SNP at the Service of Remembrance at the Cenotaph, which is about remembering the sacrifice of all those that have defended our freedoms, including members of Mr Flynn's family.
As many as 10,000 veterans and armed forces personnel took part in the ceremony, which was also attended by Prime Minister Rishi Sunak and Labour leader Sir Keir Starmer
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"It is disappointing that the Scottish Conservative Party is seeking to politicise Remembrance Sunday in this way, on a day when we should be united in remembering the service of others."
As many as 10,000 veterans and armed forces personnel took part in the ceremony, which was also attended by Prime Minister Rishi Sunak and Labour leader Sir Keir Starmer.
