Tokyo police arrested three Iranians and a Chinese on Monday for unlawfully converting used telephone cards into reusable ones for sale.
The four men, ranging in age from 27 to 38, have already been charged with violating the Immigration and Refugees Law, the Metropolitan Police Department said.
Investigators suspect that the four are responsible for having altered more than 40,000 used telephone cards each month this year alone, and sold bundles of 10 to 15 altered cards for 1000 yen on the street in Shibuya and other busy Tokyo areas.
Police confiscated some 10,000 altered cards as well as equipment and tools believed to have been used to convert them.
According to police, the Chinese man altered 9,846 used phone cards at his apartment in Tokyo's Shinjuku Ward between late May and late June.