You want to take a look at Section 10.3(e)(2) of IRS Circular 230, which says:
"(2) Practice as an enrolled retirement plan agent is limited to representation with respect to issues involving the following programs: Employee Plans Determination Letter program; Employee Plans Compliance Resolution System; and Employee Plans Master and Prototype and Volume Submitter program. In addition, enrolled retirement plan agents are generally permitted to represent taxpayers with respect to IRS forms under the 5300 and 5500 series which are filed by retirement plans and plan sponsors, but not with respect to actuarial forms or schedules."
https://www.irs.gov/pub/irs-pdf/pcir230.pdf
You should also take a look the opinion in Loving v IRS, No. 13-5061 (Feb. 11, 2014) and Section 10.32 of IRS Circular 230, which says:
"Nothing in the regulations in this part may be construed as authorizing persons not members of the bar to practice law."
Copy of the Loving opinion is online at https://www.cadc.uscourts.gov/internet/opinions.nsf/B63C3129A4FE761985257C7C00539949/$file/13-5061-1479431.pdf