"It has come to Independent's attention that Mr Pressly has recently sought elected political office with a political party, by applying to the said party's electoral college to be on its list of candidates for Parliament during the 2014 general elections," group executive editor Karima Brown said in a statement.
"Mr Pressly did this without informing his editor, and while continuing to write news as well as opinion and analysis on the said political party without declaring his political intentions to our readers."
Pressly is Business Report's Cape Town bureau chief.
Brown said if the allegation was true, it would constitute a breach of their editorial code of conduct, code of ethics, and a breach of trust.
"This and other unrelated issues are the subject of the internal investigation," she said.
‘Good citizenship to belong to parties’
Pressly said he was not allowed to comment on the matter and referred queries to his attorney, Michael Bagraim. Bagraim told Sapa his client had been honest about his political affiliation.
"He [Pressly] has admitted to belonging to the Democratic Alliance. He is not hiding the fact. He has been honest," he said.
"As citizens, most of us should belong to political parties, that's good citizenship."
Bagraim said he was not impressed by the press statement issued by Independent Newspapers about Pressly.
"I personally am very shocked. I presume journalists all over the country belong to political parties and I wouldn't expect any of them to resign or subject themselves to disciplinary inquiries," he said.
"I have not spoken to my client, Mr Pressly, as yet. I am going to be seeing him next week."
In November, Business Day reported that Sunday Times executive editor Brendan Boyle was suspended after allegedly applying to become a Democratic Alliance MP.
It reported that Boyle sent his curriculum vitae, which was later withdrawn, to the party as part of his application.
Last month, Independent Newspapers acted against Cape Times editor Alide Dasnois. She was fired after the newspaper published a front-page article on Public Protector Thuli Madonsela's finding against Agriculture, Forestry and Fisheries Minister Tina Joemat-Pettersson.
It found that the minister was guilty of maladministration and improper and unethical conduct in the awarding of an R800m tender to a Sekunjalo subsidiary to manage the state's fishery vessels.
The Cape Times is owned by Independent Newspapers, whose controlling shareholder is Sekunjalo Consortium.
Independent Newspapers' boss Iqbal Survé denied that Dasnois's dismissal was due to the fisheries tender story.
In August last year, the SA National Editors' Forum encouraged members of the public and parties to complain to the Press Ombudsman if they believed a story was written due to political or other influences.
"If members of the public or political parties suspect that a particular journalist has improper relationships and is being influenced, and that his/her behaviour is improper, they should complain to that journalist’s employer who will deal with it in line with its own policies," it said at the time.
"As Sanef, we recommend that once the name of a journalist appears, with his or her consent, on a political party’s official list of candidates to the Independent Electoral Commission, such journalist should resign his or her position as a journalist, even though they might not be guaranteed a seat after the election."