The tax code does not allow tax-exempt institutions and retirement funds to defer tax on income generated outside of their core businesses. MLP income payments are considered earned directly by the partners. Because IRAs are not in business to transport natural gas, for example, distributions from MLPs could be considered unrelated business taxable income (UBTI). This makes them immediately taxable. Usually only a portion of MLP income payments are considered UBTI. The K-1 form will split out the taxable portion.
HOWEVER:
There is a tax deduction for the first $1,000 in UBTI each year from all sources within your tax-deferred accounts. Any UBTI over $1,000 is taxed as ordinary income in the tax year it is earned.
So unless you own a ton of NS, fugetaboutit.