It's a tricky situation. I wonder what has changed. My recommendation is to capitalize on the positive results and relationship you have enjoyed previously and schedule some one-on-one time with your supplier to reconnect. At that point you can find out if the problem revolves around price, process -- or perhaps a personal issue?
But before you schedule that time, though, here are a few things we suggest you consider:
Has your pricing changed? Or maybe their cost structure has. Lately, increases such as in SUTA (State Unemployment Tax Authority) costs have affected staffing firms. Maybe your supplier is passing this cost on to you, or needs to. If your company is not bearing the brunt of SUTA, that could be causing your supplier to drive fewer candidates toward your requisitions and direct high-quality candidates to companies that offer higher margin opportunities.
Maybe it has nothing to do with price. It really could be about the vendor's performance. Has the vendor been changed to a tier 3 supplier from tier 1 due to poor performance? Such a change would definitely result in fewer job requisitions coming their way. Check the supplier's status through your MSP or VMS. Such a status change could explain the decrease in resumes. While you're at it, have that MSP or VMS give you an explanation and metrics on the supplier's past performance.
Another explanation could be a personnel change in the agency that might have affected delivery. In case you haven't noticed, this is a boom time for staffing professionals. We predict there may be some turnover and churn as CW professionals are recruited in and out of staffing firms. This could cause temporary delays and instability as new workers come up to speed on the ins and outs of your company. Make sure your suppliers provide their hires with training and integration so any changes in personnel are seamless. This can be a great training opportunity for your supplier, and even better: a chance to check in on processes that work (and don't) when engaging CW.
Meanwhile, consider whether you have a well-timed overall process for engaging contingents and bringing them on board. You could be unpleasantly surprised, don't lose good candidates because of lengthy processes and delays before they can start work. Sometimes the delay could be due to background screening or getting security clearance. Either way, it's your company's responsibility to ensure that its suppliers know your expectations up-front, otherwise, your supplier won't be able to meet them in a timely manner or may submit sub-par candidates quickly just to get some resumes in.
Once you review all of these possibilities, you should discover why your supplier is under-performing. At that point, you can take the appropriate steps to ensure that you are both getting what you need.