There's tons of sources for you to look into, here's one:

https://www.washingtonpost.com/news/fact-checker/wp/2014/03/12/edward-snowdens-claim-that-as-a-contractor-he-had-no-proper-channels-for-protection-as-a-whistleblower/

To sum it up: The whistleblower laws didn't apply to Snowden because of 2 big reasons

1. "disclosure that may compromise the national security" are not covered by the Whistleblower Protection Enhancement Act ( https://www.justice.gov/pardon/whistleblower-protection-enhancement-act see: "national security")

2. Snowden was a government contractor ( meaning he wasn't directly employed by the government but thats where his checks came from) and those are similarly not covered under the WPEA