Parents in the south London borough of Wandsworth who want to oppose partial selection in their neighbourhood have found they must appeal to local "admissions authorities" - which in some cases may be the schools themselves.
Now a group is challenging the final arbiter, the Admissions Adjudicator for England, in what is expected to be a test case.
The Wandsworth-based Campaign for Local Education wants a change in the rules so that objections can be lodged anonymously.
Schools are in the process of publishing their admissions procedures and any objections must be made within six weeks. All 10 secondary schools in Wandsworth select their pupils to some extent by ability.
John Valentine, a member of the Campaign for Local Education has written to Sir Peter Newsam, the chief adjudicator: "Parents are concerned they may be discriminated against by the school, in the event of an unsuccessful objection." He said his group would provide names to the adjudicator, but saw no reason why they should be passed on to the school.
Mr Valentine has also lodged a complaint with Charles Clarke, education minister.
While parents will not be able to object to schools who chose by aptitude, they will have a say where schools select partly on academic ability. For example. in Wandsworth, Ernest Bevin and Graveney schools select 50 per cent and Burntwood select 30 per cent.
Parents say it is impossible for many children to get into nearby schools because siblings of children at the school are also given priority.
The Campaign for State Education, which is co-ordinating the fight to abolish selection, views the parents' action as a test case to see whether the adjudicators will rule on how partial selection affects admissions in an area.
A Department for Education and Employment spokesman said that under the admissions code of practice the process must be seen to be fair and clear.
The Secretary of State has powers to intervene where there are irregularities in procedures.