MPs opposed to plans to put fluoride in public water are preparing to take the government on in court if they lose a crucial vote in the Commons next week.
The anti-fluoride committee is organising an unofficial "whipping process" to galvanise MPs to come into the House on Thursday next week, when the free vote is expected to be held.
If they lose and the bill becomes law, they will launch a legal challenge. Lawyers will argue the water bill is a breach of human rights.
The move comes after the public health minister, Melanie Johnson, wrote to all MPs. She stressed the controversial clause in the water bill was "not seeking to impose universal fluoridation".
At committee stage last week MPs voted by 14 to six to include the clause in the bill. During the report stage next week, anti-fluoride MPs will try to amend the clause to give local councils, not local health authorities, the power to decide if fluoride is added.