In Brazil Elections, they developed a modified Linux version called "UENUX" to run 570 thousand electronic vote machines, where the people go to Vote on those machines.
Since they really mixed their code with a modified Linux distribution, I presume all code is "automatically" GPL-2.0. In this case, it's mandatory to open/release the code because people are using it in the voting machine? Thanks.
(as a general question: "people that Just Use a product whose software runs under a GPL license, can require access to the source code?")