Attorney Joel P. Bennett, who represents federal employee Karen Kraushaar, 50, said he was planning the news conference with attorney Gloria Allred, who represents Sharon Bialek, 50, a Chicago homemaker, The Washington Post reported.
The Post said details of the joint appearance have not yet been worked out, but Politico said Bennett plans to hold the news conference even if other women who reportedly said they were harassed by the Republican presidential candidate do not come forward.
Bennett said he has not talked yet directly with Bialek or Allred, Politico reported.
Earlier, Bennett said Cain's behavior toward Kraushaar was harassment.
Kraushaar also said Cain, whom she accused of acting inappropriately toward her while he led the National Restaurant Association in the 1990s, could be called a "monster," ABC News reported Tuesday.
Kraushaar, whose identity was revealed Tuesday, said she had tried to avoid the media spotlight because she feared retaliation from Cain backers.
Bennett last week said his client reported a "series" of incidents involving Cain when she worked in the trade group's communications department while Cain was chief executive officer in the late 1990s. She now is a spokesperson for the IRS Inspector General.
Kraushaar left the NRA after receiving a reported $45,000 settlement.
Cain has strongly denied any wrongdoing with Kraushaar or any of the other three women who have accused him of acting inappropriately. He previously blamed fellow GOP contender Rick Perry, the governor of Texas and the "liberal" media for fueling the scandal. Tuesday blamed the "Democratic machine" for the emergence of one of his accusers.
Bennett said Cain's behavior "qualified as sexual harassment in our opinion," while not speaking about whether the alleged harassment was physical or verbal.
Since her identity was revealed, Kraushaar said she wanted to appear at a joint news conference with the other accusers.
Cain said Tuesday in a news conference he "will not be deterred by false, anonymous, incorrect accusations."
The latest allegations and plans came ahead of a nationally televised debate Wednesday among the eight Republican GOP contenders at Oakland University in Rochester, Mich. Jobs and the economy are supposed to be the focus.
GOP rival former Massachusetts Gov. Mitt Romney Tuesday called the allegations against Cain "particularly disturbing" and said, "They're going to have to be addressed seriously."
Kraushaar emerged from anonymity a day after Bialek went public with allegations against Cain, accusing him of groping her in a car in the late 1990s.