Ahmadinejad has downplayed the accusations against his ally Kordan
The Iranian parliament is debating whether to impeach the interior minister, Ali Kordan.
Mr Kordan has admitted a degree that he said came from Oxford, a prestigious British university, was a forgery.
Both conservatives and moderates MPs have called on Mr Kordan to resign or be dismissed from the cabinet.
Correspondents say that if Mr Kordan does lose his job, President Mahmoud Ahmadinejad may have to submit his whole cabinet for a vote of confidence.
The impeachment process is being seen as a major challenge to the president.
Mr Ahmadinejad has said the impeachment is illegal as Mr Kordan committed no wrongdoing while in office, the official Irna news agency reported.
"We do consider the parliament to be our ally, but we do not approve any impeachment," Mr Ahmadinejad was quoted as saying and went on to accuse opponents of being behind the calls for impeachment.
On 2 November Mr Ahmadinejad dismissed a government official, Muhammad Abbasi, after allegations that the official paid lawmakers who promised not to vote for an impeachment.
In August at Mr Kordan's confirmation, many MPs questioned his qualifications for the post but he was still approved by a small margin.
The prestigious British academic institution said it had no record of the degree.
Mr Kordan's certificate was revealed to be a crude forgery, containing several mis-spellings. He does not even have a first degree although he has worked as a university lecturer.
After he was confirmed in his job Mr Kordan made an admission in a letter to Mr Ahmadinejad who forwarded it to parliament.
The degree had ostensibly been given for his "managerial and executive experience and for submitting a thesis to Oxford University via a person who had opened an affiliate office in Tehran," the minister wrote.
He said enquiries he had made since doubts were raised had shown it was not genuine and he claimed he had filed a complaint against a missing intermediary, whom he did not name.