Insurance companies such as Standard Life and Resolution could lose out from a Financial Services Authority (FSA) probe into the £11bn annuities market, analysts said.
The FSA's two-phase thematic review, which began last month, will focus on whether consumers face detriment if they do not shop around for an annuity, and instead accept an offer from their existing pension provider.
Nick Poyntz-Wright, head of life insurance at the regulator, said: "The FCA [Financial Conduct Authority] has set out its vision to make sure markets work well so consumers get a fair deal.
"An annuity purchase is an important one-off decision that has long-term consequences for individuals if they get it wrong."
Analysts said Resolution and Standard Life are among the insurers that sell annuities mainly to their own pension customers, and therefore potentially have the most to lose from the probe.
"A successful FSA investigation would logically impact on those companies primarily selling only to their in-house customers," Deutsche Bank's Oliver Steel wrote in a note to clients. "There is a risk that in-house annuity providers such as Standard Life and Resolution lose out."
Championing diversity in the workplace
Our weekly heads-up for advisers