More than 20 current and former staff members signed a statement expressing their "disgust" over the new owner's ordering that the story be taken down from the newspaper's website.
In a page on its website where it lists the clients it has previously worked for, one of Asia PR's work is for "Cambodia and Hun Sen's entry into the Government seat".
Stuart White, the managing editor; Brendan O'Byrne, the business editor; Jenni Reid, the web editor; and Baliga all refused to comply and resigned.
The move comes after the owner of the English newspaper, which has been a frequent critic of Prime Minister Hun Sen and the last independent news organisation in the country before the sale, sacked the journalists who wrote the article and the editor-in-chief. Kay Kimsong, the publication's editor in chief, advised CNN he had been fired by the paper's new administration.
Sivakumar called the piece "a disgrace and an insult to the independence claim of the newspaper" and said it "borders on internal sabotage". The Australianmentioned the paper had been "remarkably" free from authorities interference.
In the previous year the Cambodian government closed The Cambodia Daily and dissolved the main opposition party in a wide-ranging crackdown.
"The prospects were already very bleak for a free and fair election" in July, Sam Rainsy added in a telephone interview from Paris, where he lives in exile.
This "cannot be concluded based on what happened between the firm and the client more than 25 years ago", the statement said.
"I hope this is just a blip in the history of the Post and it continues to be an independent, successful newspaper serving the Cambodian people".
The Post's sale may indicate that Hun Sun's administration has decided that it no longer needs to allow a free media to operate in the country as a concession for getting Western aid, said Shawn Crispin, the Bangkok-based Southeast Asia representative for the Committee to Protect Journalists, a nonpartisan advocacy group based in NY.
Crispin said he anxious that the tax bill The Post was facing might have been a pressure tactic used to force the newspaper's previous owner, Bill Clough, to sell, rather than fight the bill in court.
Bill, who is chairman and publisher of the Post Media Co., Ltd, said in a statement that Siva is a well respected newspaper man, with an experienced journalist background, and represents a strong investment group from Malaysia.
The new owner is Malaysian investor Sivakumar Ganapathy, an executive director at Asia Public Relations Consultants Sdn Bhd, headquartered in Kuala Lumpur.
The Overseas Press Club of Cambodia (OPCC) voiced its concerns about the sale "to a Malaysian investor whose PR company is connected to Prime Minister Hun Sen".
"Rumours about pressures from Hun Sen's government to try and muzzle the Phnom Penh Post have spread for a few months", he said. "I think the odds are greater than 50/50 the paper's coverage will change - and for the worse", he said.
The Post has also been dogged by an ongoing legal action launched by former chief executive Chris Dawe for wrongful dismissal during his tenure at the paper.
Emotions ran high in the hallways and offices of the Post on Monday afternoon after the new ownership tussled with editors over the story.