Yes! You can and should go there, in fact. But asking for a raise seems like one of the most daunting things that we do, right? I mean, it's one of those pulse-pounding sweat-inducing tasks that we put off at all costs. Why? Because we're so grateful that someone is handing us work that we don't want to seem ungrateful, nor do we want to offend the person offering said work.
Here's the thing: in any job, you'd get raises as time goes on and after you've proven yourself a valuable commodity. Writing is no different. If you feel that you deserve a raise, well, then figuratively march yourself into your boss's/editor's office and ask for one.
Here are some tactics as to how to go about it:
1) Say something like: "You know how much I enjoy writing for you. However, I earn more money writing for your competitors and was hoping that we could discuss a boost in my rate."
2) Be prepared with a number to offer. I think the best tactic to do so is to figure out how much you need or want to earn per hour for each article, and then suggest the word rate that will get you there.
3) Be kind and gracious yet still professional and firm. One of the best negotiating tips that I've read said, "Pretend that you're negotiating on behalf of a friend. You'd never allow her to get paid poorly, so do everything for yourself that you'd do for her."
4) Don't take it personally or worry that you'll be fired for asking for a boost. Most editors are actually PREPARED to raise rates if they can - the author just has to ask. And if they like you, they sure as hell aren't going to ditch you for asking. They might not be able to raise your rate, but seriously, you'll almost NEVER lose the job just for asking...and if you *do* lose a gig over getting money that you deserve, is this really an outlet you want to be associated with? (Other readers can chime in here to agree with me!)
So, those are my thoughts. Other writers out there who ask for raises, how do you go about it?