Rush Limbaugh has his head up his ass when he says:

However, our own US Congress voted themselves a raise. Many of you don't
know that they only have to be in Congress one time to receive a pension
that is more than $15,000 per month.

A single congressional term is two years.
It takes five years to vest in the Congressional pension fund, so a congressman
would need to be reelected twice to even receive a dime of pension income.

A Senator elected to a six year term would be eligible toward the end of a
single term, true.

These figures are now a few years old, but not long ago the average pension for
members of the US Congress was between $45-50,000 per year, (about $4k a month,
not $15k) and included in that average are congressmen who served for 20 or 30
years as well as those who served only a single term.

As always, Rush doesn't let the truth get in the way of a sensational lie
disguised as a statistic.

http://www.c-span.org/questions/weekly68.htm