I've been told that いや (in its use similar to いいえ) is a mainly masculine word, but I've heard many female speakers use it, both as a filler and a content word expressing disagreement. Is it that young female speakers use it these days?
When いや is used in the sense of being a casual way to say 'no', yes, it is mostly only used by men. And as Hideki says, 嫌だ meaning disgust or dislike is the other meaning. The reason I'm submitting a separate answer that says the same as his is because of potential difference in dialect.
I've been living in Tokyo for several years and I hear women(usually mid thirties and under) say 嫌だ all the time, and I have never heard a man say it. This is, of course, just my experiences, but perhaps if the other answerer is living in Kansai or something, it's a difference in trend or dialect.
If I had the reputation level to comment, this would have been appended to his answer.