Fee-only advisors who work with small companies offering 401(k) plans will now be able to offer a bundled retirement plan service from Vanguard.

Vanguard will also is offer the service directly to the companies themselves. The service is aimed at companies with less than $20 million in assets in 401(k) and profit-sharing plans, and will include Vanguard's investment and indexing services, as well as record keeping, call center services, compliance testing and participant education. It also will offer optional services, such as participant advice, and self-directed brokerage and trustee services.

To offer the service, Vanguard, which manages more than $1.6 trillion in U.S. mutual fund assets, is teaming with Ascensus, an outsourcing firm servicing the retirement plan marketplace.