Craigslist, which has been charging for classified jobs ads on its New York and Los Angeles sites since 2004, will begin charging employers a flat-rate fee of $25 per post in Boston, San Diego, Seattle and Washington, D.C.

The move is designed to weed out spam, get-rich-quick schemes and other prohibited posts, according to Media Life (via MediaBuyerPlanner). Craigslist claims that the quality of job postings on the New York and Los Angeles sites has dramatically improved since the fee was instituted. The San Francisco site also charges a $25 fee.

Smaller, nonprofit and odd-jobs listings will remain free.