Organisations "touting for business" are encouraging parents to sign up to free schools that do not yet exist, The TES has learned.
Critics have likened the situation to a "gold rush", warning that it will create "utter chaos" 21in the school admissions system.
The Department for Education says that free schools are "all ability state-funded schools set up in response to parental demand".
But senior members at teaching union the NUT and others have voiced concerns that companies are "breaking the spirit" of the process by attempting to whip up parental interest, possibly to the detriment of local schools.
One organisation in west London has been encouraging families to enroll their children in new free schools before MPs gave legal permission for such institutions with the Academies Bill this week.
To open a free school, organisations must demonstrate a "genuine, robust demand for places" in the area by giving the DfE a petition or "declaration from interested parents". They also have to show planned pupil numbers and outline how this "will support a financially viable business plan".
But ABC Academies, a charity established to run up to eight free schools in London, has delivered flyers to homes near Shepherd's Bush, west London, saying: "A new primary school for your child! We are opening a new school in your area soon and we are enrolling now."
Parents can register their child on the charity's website.
John Bangs, head of education at the NUT, said: "This is a recipe for utter chaos in the education system. It is gold-rush tactics applied to the education system. This is breaking the spirit of the procedure. It's absolutely outrageous, never mind the adverse implications for neighbouring schools of parents getting these covert messages. It's touting for business before the Queen has even given her consent."
Andy Slaughter, Labour MP for Hammersmith, west London, said: "There is no new primary school; there is only the idea of attracting children from existing schools and then applying to the Government for the money that goes to those in order to set up a new free school."
One of the key figures behind ABC Academies also runs School Plus, an organisation that lets out school buildings out of hours.
A spokeswoman for ABC said staff had been "pushing as hard as they can" to get parents to sign up because it was initially thought the free school could open in September.
After realising this would be impossible it changed the wording on the website from "enroll" to "register interest", but the leaflets had already been distributed. About 70 parents have signed up.
The charity has not met with the Government yet and will be making a formal application to set up a free school in September 2011.
"After speaking with those who have experience we knew it wasn't going to be possible to open in September 2010, but initially we thought we could have a nursery and we were pushing it as hard as we could," she said.
"The change in wording from 'enroll' to 'express interest' seemed to make parents more receptive."
A DfE spokesperson defended the flyers, saying: "It is right that groups inform local parents of plans for new schools in their area.
"We have received a number of proposals for free schools from interested groups. We are currently considering these and no decisions have been made as yet. We will publish the proposals that have been received by the department. This is likely to be in the autumn term."