The Northern Ireland Catholic Council on Social Affairs (NICCOSA), has called for the retention of the 50:50 recruitment provision for the PSNI.
However, the NI Secretary has said he is "not minded" to continue it.
In November, Owen Paterson announced details of a consultation process which is due to end in March 2011.
NICCOSA said it was not the time to remove a measure "crucial to the transformation and success of the PSNI".
The current 50-50 recruitment process was introduced to increase the numbers of Catholics joining the police.
When it was introduced in 2001, Catholics made up about 8% of the PSNI. By 2010 the level had risen to just over 27%.
However, the scheme has been strongly opposed by unionist politicians
NICCOSA said it called on people from every religious and political background to actively support those women and men "who courageously serve the safety, peace and well being of our society".
"We appeal to members of the Catholic community in particular to demonstrate their support for the PSNI by encouraging young people from all backgrounds to consider becoming members of the service.
"Serving one's society as a police officer, in a service that is representative of the community, committed to the human rights of all and dedicated to the peaceful pursuit of the common good is a noble ideal and a laudable Christian vocation which all Catholics are called to support."
NICCOSA said that the current level of Catholic membership of the police force was not "sufficiently representative" of the community composition of the workforce in Northern Ireland.
"We challenge the continued under-representation of Catholics in the senior ranks of the PSNI and call for increased efforts to encourage senior ranking police officers from police services in Britain and the Republic of Ireland to join the PSNI."
In November, Mr Paterson said he would "reflect carefully" on the outcome of the consultation.