Who may propose the registration of an initiative?

Constitution of 1917 (as amended in 2015)

Federal Law on Popular Referendum (March 14, 2014)

Article 14. Citizens who wish to file a request for popular referendum for the next immediate referendum day should submit a Notice of  Intent to the Chairman of the Executive Board of the corresponding Chamber with the corresponding format defined by said Chamber for such purpose.

The Chairman of the Executive Board of the corresponding Chamber will issue with  in ten working days, a document certifying the submittal of the Notice of intent, that will include the format to obtain signatures, and with that the beginning of the acts to collect support signatures. The notification  record will  be published in  the Parliamentary Gazette.

Failure to present the Notice of intention will be deemed as a cause not to admit a request for popular referendum. The formats, Notices of intent and certificates issued will be effective only for the popular referendum held at the next immediate referendum day.

The law only states that "citizens" can file request for a referendum. There are no further requirements.