Europol has announced the arrest of 19 people engaged in forging or altering European passports and visas.
The purpose of the criminal operation was to facilitate illegal migration to the EU, authorities said.
Two major Europol operations saw 16 people arrested in Greece and three in the Czech Republic over forged documents for migrants, authorities announced on Tuesday.
Working in tandem with national police, the international law enforcement group uncovered a vast criminal network involved in the "massive production" of falsified or forged passports and visas.
"The forged documents were subsequently provided to irregular migrants to enter the EU or to legalise their stays there," according to the Europol statement.
Authorities identified two large criminal organizations in Athens, composed of Bangladeshi and Sudanese nationals, "operating in parallel" to produce forged passports, Schengen visas, and residence permits.
They were then distributed through courier companies to other EU nations as well as countries in the Middle East, Asia, and Africa.
These fake documents were then sold for 100-3,000 euros ($111-3,340) "depending on the quality, type and country of issue."
The smaller Czech syndicate was operating mostly with stolen or lost travel documents which they then altered.
Europol Director Robin Wainwright said that "in the last two years we have seen criminal gangs increasingly investing more in the production of fake documents to support a growing criminal market associated with the migrant crisis. Document fraud is now a highly important enabler of organized crime."
The huge operation saw the participation of 19 EU member states as well as the assistance of US Immigration and Customs Enforcement.