Bilston great grandmother Patricia Drew says she was stunned when copyright holder TCYK LLC wrote to her accusing her of pirating the box office flop The Company You Keep.
Mrs Drew's son, Dave, from Dudley, described the American firm's claims as 'laughable' and said his mother barely knows how to turn on the computer.
He has called for lawmakers to plug 'a legal loophole' allowing firms to exploit unsuspecting members of the public.
Dudley North MP Ian Austin has joined the fight. He has written to Business Secretary Sajid Javid calling for action to protect consumers and vowed to raise the issue in Parliament.
Mr Drew, aged 59, said: "My mother can just about manage to turn the computer on and generally uses it to play solitaire.
"She has a Facebook page which was set up for her but she doesn't really know how to use it.
"It is frankly quite laughable that anyone could accuse her of downloading a film."
The letter was sent last month and accuses Mrs Drew of infringing copyright by downloading the film at 2.11am on April 25, 2013.
It said that if she accepted liability and paid a settlement of £600 she could avoid having to attend court. The firm sent her a letter containing similar information last November.
TCYK LLC, which has initials that are an acronym for the film's name, successfully launched a court action ordering Sky to provide details of account holders matching a specified list of IP addresses.
The firm is then alleged to have instructed financial services firm Hatton & Berkeley to send out thousands of letters to Sky broadband customers demanding payment for illegally downloading the Redford film.
Robert Croucher, managing director of Hatton & Berkeley, said the letters were part of a 'pre-action protocol', which occurs before legal action is enacted. "They don't actually make a demand for money," he added.
But Mr Drew said: "They have provided absolutely no factual evidence that she downloaded this film, yet the tone of the letters is very threatening. You can imagine that a lot of people would get scared into paying.
"My mother is stunned by what is going on but there is no way we will be paying up.
"The crazy thing about all of this is that by all accounts this company are operating within the law. They are threatening people with legal action, which in my mother's case at least is over a false accusation of wrongdoing, and causing a great deal of unnecessary worry.
"It is clearly a loophole in the law that allows them to behave like this. The only way this will stop is if our lawmakers step in and take action."
Ian Austin said he was disgusted to hear that a Black Country pensioner was being 'bullied and hounded for compensation'.
"This company has made a ludicrous allegation," he added. "I am waiting to hear from the Business Secretary to see what action the Government plan to take on this disgraceful behaviour."
Mr Austin added that he had also written to TCYK LLC urging them to rethink their case. He said he has yet to receive a response.
A statement on the firm's website thanked Mr Austin for addressing the issue. "We are still very concerned about the theft of our intellectual property," it added.
The Citizens Advice Bureau has warned of the rise of so-called 'speculative invoicing', which it said may be founded on 'a number of misleading claims'.
Michael Coyle, a solicitor-advocate with Lawdit Solicitors, who is advising Sky Broadband customers, said he had been approached by at least dozens of people who received similar letters – most of whom deny piracy.
The Company You Keep, a 2012 film about former Weather Underground activist who goes on the run, went straight to DVD in the UK and took just $5m at cinemas in the US.
American firm Antonelli Law says TCYK LLC has filed dozens of copyright infringement lawsuits in the federal courts of Illinois, Indiana, Colorado, Florida, Minnesota, Ohio, Tennessee, and Wisconsin involving the same film.
Sky broadband customers have previously been targeted by Golden Eye International (GEIL) over alleged copyright infringement.