The national suicide prevention helpline has introduced a new crisis category as it prepares to take more calls relating to the same-sex marriage plebiscite.

Volunteers at crisis support helpline Lifeline are asked to enter the "main reason" for a call when dealing with people seeking help, and one of the options now reads "2016 Marriage Equality Plebiscite".

A spokesman for the 24-hour helpline said the category had been "recently" introduced. It is understood categories are updated when there is an increase in the number of calls relating to the subject.

However, a spokesman for Lifeline could not confirm whether calls to the service about the plebiscite had increased, because the organisation has only just begun to collect the data.