Narain had applied for three weeks' earned leave so that she can campaign for the polls slated for August 27. Thampu had turned down the application, saying "cannot oblige".
Narain has shot off a letter to Thampu warning him of legal action if her application was not considered "within 24 hours".
"DUTA elections are due to be held on 27 August, and I am seeking a second term. Three weeks of leave is the minimum I would require in order to cover the varsity which is spread over all seven Lok Sabha constituencies (of Delhi)," Narain said in her letter to Thampu.
The fresh development comes against the backdrop of Thampu indirectly attacking Narain in connection with a molestation row involving a Stephen's research scholar, when he had accused the DUTA chief of being one of the "handlers of the controversy".
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The two have been at loggerheads in the past as well with Narain dragging Thampu to court for ordering an institutional inquiry against her for allegedly defaming the institution.
"Because of this, I have been repeatedly targeted and have faced continuous harassment by you. In one such instance, I have even been compelled to seek legal redress for my protection," she said.
Thampu was not available for his comment on the issue.