回复：感觉不是B的trap，你如果因此被砍B也拿不到钱....

Very good analyses. I agree with these arguments than other ones offered by other posters. As a matter of fact, I had an experience as a contractor to share. My manager was a very nice person, so he directly told me that he is the person to talk to about promotions (increases of pay rate) when I started. I was shortly converted into a permanent employee though. I guess you can ask your contracting firm to negotiate the increase on your behalf, but sometimes it may be better to do it yourself, for reasons such as 你在A那边工作很久，很多人/过程很熟悉，可能更适合提这种要求, etc。Since you've been working there for many years, I would think it's pretty reasonable to ask for it. But it defintely depends on the situation. Anyway, be realistic about what to expect.