If I'm understanding the JSON standards correctly, tabs are not allowed. I'm posting a json to my api (the whitespace at the end of the value is a tab character). This is what's happening in the background:

String string = {"key":"value "};
JSONObject json;
try {
json = new JSONObject(string);
} catch (JSONException e) {
}

the assignment above should not succeed, but it does.
you can use this sample project to see for yourself
https://github.com/mmoghadas/gs-rest-service/blob/master/complete/src/main/java/hello/GreetingController.java#L26

git clone git@github.com:mmoghadas/gs-rest-service.git
cd gs-rest-service/complete
./gradlew build
java -jar build/libs/gs-rest-service-0.1.0.jar

http://www.ecma-international.org/publications/files/ECMA-ST/ECMA-404.pdf
Insignificant whitespace is allowed before or after any token. The whitespace characters are: character
tabulation (U+0009), line feed (U+000A), carriage return (U+000D), and space (U+0020). Whitespace is not allowed within any token, except that space is allowed in strings.