In a letter to the commission, Camelot said it might apply for a review of the regulator’s decision not to revoke or suspend the Health Lottery’s licence.
Camelot alleges that the Health Lottery is in breach of the Gambling Act 2005, which allows "society lotteries" to band together under one brand providing they are independent entities.
Camelot alleges that the 51 community interest companies linked to the Health Lottery are not separate entities because they share the same directors and registered office.
Other lottery legislation permits the existence of only one national lottery.
A statement from Camelot said it had first written to the commission in October to raise concerns about the lawfulness of the Health Lottery.
It wrote to the commission again a fortnight ago saying it reserved the right to issue judicial review proceedings if the commission did not provide a satisfactory response to its latest letter by today.
Camelot said it was "required to maximise returns to National Lottery good causes in a socially responsible way. We – and potential good cause beneficiaries and the many other stakeholders in the National Lottery – would therefore be very concerned if those returns were to be adversely and unfairly affected by any unlawful scheme, as we believe is the case with the Health Lottery.
"Given that we have asked the commission for a formal response within 14 days prior to issuing legal proceedings, it would be inappropriate for Camelot to comment any further during this period."
In a statement, Martin Hall, chief executive of the Health Lottery, said: "This is an issue between Camelot and the Gambling Commission. We have seen nothing new in the arguments put forward and we believe this is without merit."
A spokesman for the Gambling Commission said it was considering Camelot’s correspondence and would respond in due course.
He said government ministers had asked the Gambling Commission and the National Lottery Commission, which regulates Camelot, to examine the impact of multiple society lottery schemes on the National Lottery and other society lotteries. The results of the study are expected in the summer.