The push for more coordinated regulation comes as the GAO has pointed out that jurisdiction for MEPs is a somewhat messy business, despite the growth in their popularity.

The DOL regulates MEPs and their participant protections under ERISA, while the IRS handles their preferential tax treatment under its own codes; the GAO notes that ERISA's requirements are to a higher standard than the IRS code, and neither entity coordinates on its varying oversight for the plans.

The upshot is considerable compliance and fiduciary challenges for those retirement professionals trying to handle the complexities of the MEPs. One open MEP may only be required to file a single annual report with the IRS but still be required to file multiple annual reports for each of its component plans with the DOL.

The GAO notes that while there's plenty of information on the sponsor types handling the largest MEPs – large corporations, associations and third-party professional employer organizations – there's less known about open MEPs, in which employers with no common relationship or affiliation share a DC or DB system.

The topic was part of the discussion at last month's ASPPA annual conference, with Drinker, Biddle & Reath attorney Bruce Ashton and Adam Pozek of DWC ERISA Consultants both agreeing that open MEPs can be tricky to administrate, given the varying opinion from both governing bodies. Are they a single plan, or are they a messier collection of plans.

Ashton said the options provided by MEPs to share the costs and provide retirement benefits otherwise impossible to do on their own do make them a valuable tool, but the DOL seems to continue to stress that that they form an aggregation of individual plans and demands a much higher standard.

To that end, he said the DOL looks for commonality (a common employment bond, such as companies that are members of a local Chamber of Commerce) and also control – responsibility for the plan must be exercised either directly or indirectly by the participating employer.

Recent DOL advisory opinion has dictated that no two unrelated employers can co-sponsor a single ERISA plan unless those commonality and control factors are included.

"Philosophically, I wonder why the DOL has taken this position, as the benefits outweigh the concerns," he said. "I guess it could be worries about abuses by the service provider, or also concern that the employees who take part are not sufficiently engaged. I always counter that employers are in the business of running their business, not their retirement plan."

In the end, what are the advantages of MEPs? Adam Pozek said the arrangements can be less burdensome to small employers and also mean that the plan sponsor or retirement advisor involved really does get to choose their own investment options.

"There's also group buying power, due to a larger pool of assets and the fact that the employees share expenses," he said. "But it can also be a bit like Costco – it may be a really good deal but you end up buying stuff that your employees really don't need."

On the downside, Pozek said MEPs' collective operational structure do create potential issues for all involved.

"It's the one bad apple problem – one adopter with a compliance problem can impact everyone involved, so they're only as good as the ability and willingness of the promising employer to pay their share, and how do you enforce that?" he asked. "Sometimes, bigger is not better."

As a further complication, each separate employer taking part in an MEP also needs to be tested for non-discriminatory testing. Both experts noted, however, that in the end, filing a 5500 for those participating in an MEP is relatively easy.