The Black First Land First (BLF) movement has tried to stop the parliamentary inquiry into state capture at Eskom.
On Friday, public enterprises portfolio committee chairwoman Zukiswa Rantho told MPs the inquiry had received a letter, threatening court action if it did not halt its investigations.
"We have received a letter from the Black Land First movement, asking the committee to stop the inquiry as of yesterday [Thursday] at 1pm. If not [the letter warns], we will be taken to court."
The letter was addressed to her, the committee secretariat, as well as National Assembly Speaker Baleka Mbete.
Rantho said she would not read out the letter.
Responding, DA MP Natasha Mazzone described the letter as "blatant intimidation", and showed a poor understanding of the Constitution and parliamentary procedure.
"We do not scare easily," she said.
ACDP MP Steve Swart said the committee would not let anyone intimidate it.
He also revealed the title of letter: "Stop the witch hunt of the Gutas and let the judicial commission of inquiry into state capture run its course."