Human rights groups are raising the alarm over EU plans to expand its database of asylum seekers.
A coalition of 31 groups including Amnesty International fears that the database, known as Eurodac, could be used to spy on migrants.
Brussels wants to beef up the database and extend it to child migrants as young as six. It would store the names, facial images and identity documents of asylum seekers, in addition to the fingerprints that are currently collected.
Activists say the reforms risk undermining the fundamental rights of migrants arriving in the EU.
“If approved, these changes would contribute to the wholly unjustified mass surveillance of migrants,” they said in a letter to Members of the European Parliament (MEPs).
“The proposed use of facial recognition for biometric identification is intrusive, disproportionate, and privacy-invasive.”
The database was set up in 2003 to help enforce the Dublin Regulation, which says people should seek asylum in the country they arrive in.
Talks on a new pact have led to stalemate in Brussels. An overhaul proposed last year called for Eurodac to be widened into a full-scale “asylum and migration database”.
Brussels says this would allow the monitoring of “secondary movements” of migrants who did not seek asylum when they entered the bloc.
It argues that registering minors will make them safer by helping authorities to find them if they go missing.
But activists say the plans to fingerprint young children are unjustified. Only over-14s can be registered under existing rules.
“Taking and retaining the biometric data of children for non-protection related purposes is a seriously invasive and unjustified infringement on the rights of the child,” the human rights groups said.
“It contradicts UN guidance that arguments based on migration control cannot override best interests considerations.”
The Eurodac reforms have yet to be approved by the European Parliament and the letter urged MEPs to put the legislative process on hold.
Negotiators reached agreement on another part of the package, the creation of a European Union Agency of Asylum, during the summer.
There has also been agreement on new rules for skilled workers, with other changes still under discussion.
It comes as European leaders are concerned about a new surge of migration from Afghanistan after the country fell to the Taliban.
Politicians want to prevent a repeat of the 2015 crisis which saw more than a million people cross the EU’s borders.
The EU wants to help Afghanistan’s neighbours such as Uzbekistan and Tajikistan to prevent large numbers of people from reaching Europe.