All households in Japan that possess a TV set are legally obliged to pay subscription fees to NHK regardless of whether they watch the public broadcaster's programs. An engineering professor at Tsukuba University is now challenging that, with a device that filters out NHK's broadcast signal.

Around 130 of the devices have been sold so far, mostly through online retailers, according to Hideki Kakeya, an associate professor of systems engineering at Tsukuba University in Ibaraki Prefecture. He developed the device with students.

One filter user, a member of the municipal assembly in Funabashi, Chiba Prefecture, filed a lawsuit June 1 demanding that NHK acknowledge he has no legal obligation to pay the fees.