The statistical basis for direct federal tax which the Federal Tax Administration (AFC) can use is insufficient. Therefore, the estimate of the number of people affected by the so-called “marriage penalty” remains rough. This is what emerged from an external report commissioned by the Federal Department of Finance (FDF). At its meeting on 7 November 2018, the Federal Council was informed of the results of this investigation.
Source
https://www.admin.ch/gov/it/pagina-iniziale/documentazione/comunicati-stampa.msg-id-72845.html