It could, but it doesn't have to. Most defined contribution plans that employers provide today would have an employer component, but part of the thinking behind expanding coverage is that for small business owners, for example, who simply can't afford to provide a pension plan or don't want the costs and complexity of providing a pension plan, why not let their employees contribute to a pension plan in any event?
It doesn't have to be sponsored by that employer. It could be a multi-employer plan, which we've heard some talk of today. Current tax rules don't permit that, though.