A "coalition for a humanitarian Switzerland" has announced it will launch a referendum against tough new laws on asylum seekers approved by parliament.
The coalition says the revisions breach the 1951 Geneva refugee convention and violate international law.
Under the new laws, rejected asylum seekers would no longer receive social welfare payments and could be detained for up to 18 months before deportation.
"The revised asylum law is a law against asylum," said Daniel Bolomey, head of the Swiss branch of the non-governmental organisation Amnesty International.
The coalition comprises representatives of churches, aid agencies, refugee and human rights organisations.
It accuses parliamentarians of losing their sense of moderation and creating a law aimed primarily at combating abuse of the system rather than offering protection to those who need it.
The legislation, which had taken three years to prepare, was officially adopted by both houses of parliament last Friday.
The coalition is politically independent, but Jürg Schertenleib from the Swiss Refugee Council said it would liaise with the centre-left Social Democratic Party and the Green Party, who had already announced that they would launch referendums.
Supporters of the changes, including the centre-right Christian Democratic Party and the Radical Party, believe they will provide better protection against abuse of the asylum system.
Asylum applicants without identity papers would have to prove that they are not responsible for that situation.
The UNHCR is particularly concerned that only valid travel documents or identity papers would be accepted. It said many asylum seekers were not able to obtain such papers before fleeing their countries.
Beat Meiner, head of the Swiss Refugee Council, said this violated the Geneva Convention on refugees and would make the creation of papers harder or impossible.
Jürg Krummenacher, head of Catholic charity Caritas, said missing papers were often a sign that the person was being persecuted.
In another criticised change, rejected asylum seekers would have their social welfare payments stopped. The aim is to speed up deportation of rejected asylum seekers.
However, cantons will be allocated SFr15,000 ($11,640) per case, to enable them to provide emergency assistance to rejected asylum seekers still in the country.
Verena Bürgi-Burri, from a Swiss women's association, said this risked throwing the old, the ill and families out onto the street and forcing them into poverty.
Coalition members feared that young asylum seekers would be more likely to go underground and be at greater risk of exploitation and child trafficking.
The law also contains new restrictions on family reunification. Asylum seekers admitted on a provisional basis would not have the right to bring their families to Switzerland until three years had passed.
The Swiss Red Cross, which is not a member of the coalition, described the laws as "inhumane" and "going against the principle of humanity".
swissinfo with agencies
The coalition includes the Swiss Refugee Council, Amnesty International, Terre des hommes and various aid agencies.
The Social Democratic Party has already announced its intention to launch a referendum against the revised asylum laws.
Measures confirmed by the House of Representatives include dropping admission to asylum seekers on humanitarian grounds and exclusion from asylum procedures for most of those arriving without valid identity papers.
The House also ruled out social welfare for rejected asylum seekers.
But it stopped short of cancelling emergency assistance to those remaining in Switzerland after a negative decision, in line with a Federal Court ruling.
The House raised the maximum detention for foreigners awaiting deportation to 18 months for adults and nine months for minors over 15.