FORTUNE -- Dear Annie: After losing my job in 2011, when my department was eliminated in a restructuring, I decided to go out on my own and do web design and SEO consulting on a freelance basis. It’s been great, except for one big problem. Over and over, I do the work, the client is happy with it, everything’s cool, but I end up waiting and waiting to get paid -- and, in a couple of cases, have not been paid at all despite repeated, polite reminders.
I’ve been lucky enough to get most of these gigs through my network of friends, and friends of friends, so I don’t want things to get nasty. (For example, I really don’t want to take anybody to court.) But I have bills and expenses like everyone else, so the suspense over when, or whether, I’ll get paid is making me crazy. Is this a common problem for freelancers, or am I doing something wrong? Do you have any suggestions? — Broke in Boston
Dear B.B.: I’m sorry to report that your dilemma is not at all unusual. One recent study of self-employed people in New York state, for instance, found that 316,000 of them (about 35%) were paid late at least once during the preceding year, and some 214,000 (14%) did work for one or more clients who never paid them at all. Total lost wages in the Empire State alone, over a 12-month span: More than $3 billion.
“Delays in payment usually aren’t deliberate on the client’s part,” notes Sara Horowitz, who founded and runs Freelancers Union, a Brooklyn-based nonprofit association that offers health insurance and other resources to the self-employed. “It’s just that your invoices get lumped in with all the other accounts payable -- and, especially since the recession, more companies are pushing those out beyond 30 days to 60, or even 90.”
Intentional or not, she agrees with you that the damage to individuals’ livelihoods is “not acceptable.” In response, the Freelancers Union drafted a bill called the Freelancer Payment Protection Act, now wending its way through the New York State legislature, that would give the self-employed many of the same remedies for non-payment that regular employees now have, including the right to file grievances with the state department of labor.
With the U.S. freelance population now at 42 million and growing, Horowitz expects that other states will eventually adopt similar measures. In the meantime, though, and before you hire a lawyer or a collection agency, Horowitz -- who, incidentally, wrote a terrifically useful book called The Freelancer’s Bible — has six suggestions.
1. Include payment terms in a written contract up front
If you’re getting most of your assignments from friends, maybe you aren’t formalizing contracts in writing, but you should. (Freelancers Union’s web site has a free customizable contract you can use.) “Negotiate a time limit. If their policy is 90 days and yours is 30, maybe you can agree on 60,” says Horowitz. “The contract can also specify a late fee, usually a percentage of the total amount.”
2. Get a portion paid before the project is finished
To help even out your cash flow, and since you're committing your time and effort in advance, Horowitz recommends charging some “earnest money” when the contract is signed, or payable at an agreed upon point in the project -- say, when the work is half complete. Not only are partial payments often more digestible for clients, but they give you an early warning that you may be wasting your time on a deadbeat: If you don't see a check at the halfway mark (if that was the deal), are you sure you want to finish the job?
3. Practice prompt, preventive invoicing
“You should send invoices right away, while everyone’s in love with your work,” Horowitz says. “No love? All the more reason to bill them and close the books.” Invoices should be sent “in triplicate,” she adds. “Send each invoice by snail mail, email, and with a phone message saying the invoice was sent. If this is what you do on Round One, let them imagine what Round Two and Three will be like.”
4. Get acquainted with someone in accounting
“You’ll glean information about their procedures and get to know someone in a position to help if there’s a delay," says Horowitz. "It's also helpful for keeping your primary work contact unsullied by the money thing.” When starting each new gig, she advises, say something like, “I know you’re busy. Is there someone in accounts payable I could reach out to?”
5. Consider delegating your billing to the cloud
“This is one time when making things less personal can really help,” says Horowitz. “Documentation is nine-tenths of the collection game, so think about hiring an online service to track your time on projects, send invoices for them, including late-payment follow-up, and handle payment transactions.” You can find these services by searching under “online invoicing” or “online billing.”
6. Have a follow-up system
“Start with an email, friendly but firm, pointing out that your invoice hasn’t been paid,” says Horowitz. “If there’s no response, a more formal notice could be next, recapping the billing information and saying, ‘This payment is now however-many days, or weeks, late. Please contact me to discuss this serious matter.’ Keep your tone professional, factual, and solution-oriented.”
It’s important to keep track of every contact with clients, she adds: “If you and the client work out a payment plan -- where, for example, you agree to accept the balance due in installments instead of all at once -- summarize it in an email for the record. Keep copies of every letter and email and a phone log. You’re building documentation for possible use in court, or to hand over to a collections agency, if it comes to that.”
Making sure you get paid may sound like a second job on top of your regular work, which is why many freelancers put off dealing with it, but that’s a mistake. “Don’t procrastinate on follow-up,” Horowitz says. “The older the debt, the harder it will be to collect.” Good luck.
Talkback: If you’ve done freelance work, or are self-employed now, did you ever have trouble getting paid? What did you do about it? Leave a comment below.