With the announcement of the press conference published on Tuesday the title was also announced for the first time: the declaration is entitled "Dignitas infinita" ("Infinite Dignity").
Prefect of the Faith Víctor Manuel Fernández had already announced in various interviews since the beginning of the year that the document would be published at the beginning of April.
It should contain a "clear criticism of the immoral tendencies of today's society".
It deals "not only with social issues, but also a strong criticism of moral issues such as gender reassignment, surrogacy and gender ideology", said Fernández told the Spanish news agency EFE.
The announcement does not provide any new details on the content of the letter.
A fundamental letter from the Vatican dealing with gender issues has been awaited for years.
Most recently the Congregation for Education published a paper on the topic in 2019which distanced itself from gender concepts that advocate "manipulation of the body at will".
Pope Francis also regularly expresses his rejection of an alleged "gender ideology", most recently at the beginning of March.
At the same time, there are repeated signs of liberalisation.
Last autumn, the Dicastery for the Doctrine of the Faith published a letter on the question of admitting queer people as godparents and witnesses to marriage and on the baptism of trans people.
Cardinal Fernández, the secretary responsible for the doctrinal section of the dicastery, Armando Matteo, and the professor of medicine Paola Scarcella have been announced as participants in the press conference scheduled for Monday at 12 noon in the press room of the Holy See.
Scarcella teaches at the Department of Biomedicine and Prevention at the University of Tor Vergata in Rome.
Her research interests include the epidemiology of ageing, HIV/AIDS and nutrition.
She volunteers in catechesis for people with disabilities in the Community of Sant'Egidio.