> Space station crews launching on Russian Soyuz spacecraft have to make their way to the Central Asian spaceport of the Baikonur Cosmodrome in Kazakhstan. No matter what the mission, even astronauts have to go through customs, NASA officials said. As part of their routine airline flights to other countries and back, they of course encounter airport customs.

It's not to/from the ISS that's the issue there.

A US-only crew on a US-launched spacecraft that lands in US territory won't need to do it. (ISS may add a few complexities, but if you stay on, say, the Shuttle, you're not leaving US-controlled territory.)