Former assistant editor Ian Edmondson and chief reporter Neville Thurlbeck have both lodged papers against the publisher, BBC News reports.
Thurlbeck, the paper's former chief reporter, is to allege at a preliminary hearing this Friday at the East London Tribunal Service that he was unfairly dismissed for whistleblowing.
However, a spokeswoman for News International confirmed that the company would "vigorously contest the case".
Thurlbeck is among three News of the World journalists - alongside Ian Edmondson and James Weatherup - to have been arrested on suspicion of phone hacking. They have all been bailed until March 2012.
In total, 16 people have been arrested so far in the Metropolitan Police investigation into allegations of illegal voicemail interception at the paper, which was shut down in July.
An email apparently intended for Thurlbeck, known as the "for Neville" email, has become a key piece of evidence in the phone hacking probe as it appears to debunk News International's claims that the practice was down to just one "rogue reporter" at the News of the World.
News International chairman James Murdoch has been recalled to give more evidence to MPs after his claim that he was not aware of the "for Neville" email before signing off a major phone hacking settlement was contradicted by other staff at the paper.
Separately, former News of the World editor Andy Coulson is suing News International subsidiary News Group Newspapers for alleged breach of contract after the company stopped paying his legal fees.
> Labour MP says The Sun should face phone hacking questions