"The bail applications are dismissed. Both the accused be taken into custody forthwith," Special CBI Judge O P Saini said.
The court directed that 43-year-old Kanimozhi and Kumar should be produced before it at 10 am tomorrow, when the case comes up for hearing.
The DMK MP, wearing an orange salwar suit, looked stunned after the CBI judge pronounced his order and was consoled by her family members, including her husband Aravindan.
DMK leaders, including its parliamentary party chief T R Baalu, was present in the court.
Minutes after the court pronounced its order, some of DMK supporters broke down while others were seen making frantic calls.
The court in its 144-page order said that most of the witnesses against the DMK MP are the employees of Kalaignar TV and hence the possibility of they being influenced cannot be ruled out.
"Considering the magnitude of the crime and the fact that many of the witnesses are employees of Kalaignar TV, there is every apprehension that the witnesses may be influenced, if the accused are released on bail," the CBI judge said.
The court also considered the "enormity" of the offence while rejecting the bail of Kanimozhi and Sharad Kumar.
"Considering the magnitude of the crime, nature and enormity of the allegations, character of evidence on record and the apprehension that the witnesses may be influenced in case the accused are released on bail, I have no hesitation in holding that both applicants/accused have failed to make out a prima facie case for bail. Bail applications are without merit and the same are dismissed," the judge said.
The court, however, clarified that its observations were "tentative" and they do not express any opinion on the merits of the case.
The CBI had chargesheeted Kanimozhi on April 25, for her alleged role in the 2G spectrum allocation scam. It had indicted her for taking a bribe to the tune of Rs 200 crore, which was routed to Kalaignar TV, in which she has 20 percent stake.
The money was routed to the TV channel by DB Realty of Shahid Usman Balwa, who was of one of the beneficiaries of the 2G spectrum allocation scam, with his another firm, Swan Telecom, securing the 2G spectrum licence during the tenure of former Telecom Minister A Raja of her party.
Besides Kanimozhi, former Tamil Nadu Chief Minister Karunanidhi`s wife Dayalu Ammal holds 60 per cent share in the Kalaignar TV. She, however, was not chargesheeted in the case as the CBI said she did not take part in the day-to-day functioning of the channel.
Kanimozhi was chargesheeted along with TV channel MD Sharad Kumar, who too held 20 percent stake in it.
After the CBI filed chargesheeted against them in the Special CBI court, they were asked to appear before it on May 6, when Kanimozhi filed her bail plea.
The court earlier had reserved its verdict on her bail plea for May 14, but had advanced it to today.