The House of Representatives Disciplinary Committee voted unanimously Wednesday to summon Takashi Nishizawa, named by lawmaker Hisayasu Nagata as the middleman who gave him the fake Horie e-mail, for sworn testimony on April 4.

The fake e-mail purported to show a shady financial link between Livedoor Co. founder Takafumi Horie and a son of Liberal Democratic Party Secretary General Tsutomu Takebe.

"We have come to the conclusion that Nishizawa's testimony is essential (for the committee) to decide on the penalty" for Democratic Party of Japan member Nagata, the committee chairman, Tetsundo Iwakuni, said.

In unsworn testimony to the panel Friday, Nagata said Nishizawa, a journalist, gave him the e-mail that he read out in February in the Diet in a bid to discredit Takebe. The DPJ later apologized, followed by Nagata, after admitting the e-mail was fake. Nagata now faces punishment by the disciplinary panel.

Nishizawa, through his lawyer, has denied being the conduit for the e-mail from an as-yet unidentified source.

Nagata said he believed the e-mail, which appeared to be from Horie asking his staff to transfer money to Takebe's son before the September general election in which Horie was running, to be real.

The DPJ punished Nagata by temporarily suspending his membership.

Nishizawa's lawyer Monday submitted a written statement to the panel requesting that the journalist not be summoned because he is not a politician.

However, Iwakuni countered by saying others who are not politicians have been called before the Diet.