Home Secretary Suella Braverman is facing questions about her future after defying Downing Street over an article accusing the police of bias.
She claimed aggressive right-wing protesters were "rightly met with a stern response", while "pro-Palestinian mobs" were "largely ignored".
The article was not cleared by Downing Street and suggested changes to the text were not followed, No 10 said.
Some Tories have called for the home secretary to be sacked.
It comes ahead of a Pro-Palestinian march for a ceasefire in Gaza, which is due to take place in central London on Saturday.
Labour leader Sir Keir Starmer accused Mrs Braverman of undermining the police and said Prime Minster Rishi Sunak was "too weak to do anything about it".
Former Conservative minister Sir Bob Neil became the first Tory to publicly call for her to resign over the article.
Sir Bob, a frequent critic of Mrs Braverman, told LBC that her position was "untenable" after she had "gone over the line" with her comments.
But Conservative MP Danny Kruger - an ally of Mrs Braverman - denied the home secretary was interfering, and said she was entitled to comment on the "broader culture of police".
The prime minister's spokesperson said Downing Street was "looking into what happened" over the article - but they added Mr Sunak had full confidence in the home secretary.
The ministerial code says all major interviews and media appearances, both print and broadcast, should "be agreed with the No 10 Press Office".
The prime minister can punish a minister who is deemed to have breached the code. Options can range from demanding a public apology to sacking them.
Mrs Braverman, who is popular on the right of her party and seen as a possible future Conservative leader, often takes a harder line than many of her colleagues on issues such as crime and immigration.
She has recently been criticised for calling pro-Palestinian rallies in London "hate marches" and has described being homeless as a "lifestyle" choice.
This latest row comes before the Supreme Court is due to give its decision on whether government plans to deport asylum seekers to Rwanda are lawful next week.
Mrs Braverman has been a vocal backer of the Rwanda scheme, which is part of Mr Sunak's plans to curb the number of migrants crossing the English Channel in small boats.
Police have said they expect a large rally on Saturday, prompting fears of violent clashes with counter-protesters.
Saturday is also Armistice Day, the anniversary of the end of World War One, which has prompted calls from the prime minister and others for the Pro-Palestine march to be cancelled, on the grounds that it is "disrespectful".
The Met Police has faced calls to ban the march - but commissioner Sir Mark Rowley said protests may only be stopped if there is a threat of serious disorder, and that the "very high threshold" has not been reached.
In her Times article, Mrs Braverman claimed that there was "a perception that senior officers play favourites when it comes to protesters".
"Right-wing and nationalist protesters who engage in aggression are rightly met with a stern response yet pro-Palestinian mobs displaying almost identical behaviour are largely ignored, even when clearly breaking the law," she added.
There have been regular protests in London after Hamas gunmen launched an unprecedented assault on Israel from the Gaza Strip on 7 October, killing more than 1,400 people and taking more than 200 hostages.
Israel has been carrying out strikes on Gaza since then in response, and has now also launched a ground offensive. More than 10,500 people have been killed in Gaza, according to the Hamas-run health ministry.