The cooperatives that offer CDs are facing record low yields and being cautioned to pay close attention to several factors. For example, based on recent reports of email scams aimed at CDs, regulators have warned investors not be tempted by promotions touting high yields.

Credit unions are also looking closely at penalties for early withdrawal, which vary greatly depending on many factors, including the institution's size.

Among the largest U.S. financial institutions, 90% may keep part of the principal if a customer makes an early withdrawal and the accrued interest is less than the penalty, according to a new Bankrate.com report.

The firm's “2014 Early CD Withdrawal Penalties Survey” measured early withdrawal penalty policies on 3-month, 6-month, 1-year, 2-year and 5-year CDs from May 5-14, 2014, at the top 10 banks and thrifts in the 10 largest U.S. cities, and at the nation's five largest credit unions, the report said.

The survey found that the most common penalties were three-months' dividend for CDs with maturities of less than a year, six months for CDs with maturities between one and five years, and a tie between six months and 12 months' dividend for a 5-year CD, according to Bankrate.com.

That is a change from 2012, when the most common penalty in all categories was six months' interest, said Greg McBride, Bankrate.com's chief financial analyst.

McBride said the latest survey shows an even split between the penalty applying only to the amount withdrawn or to the entire amount of the CD, regardless of how much is withdrawn.

In addition, the penalty terms are the same whether the CD is held on a taxable basis or in an IRA, he said.

The steepest penalties are more likely to be on lower-yielding offerings, especially for CDs that mature in fewer than five years, McBride said. The grace period on automatically renewable CDs is typically either seven or 10 days, depending on the account.

Both the 2012 and 2014 surveys included the five largest credit unions: the $58 billion Navy Federal Credit Union in Vienna, Va.; $28.4 billion State Employees' Credit Union in Raleigh, N.C.; $17.6 billion Pentagon Federal Credit Union in Alexandria, Va.; $11.9 billion BECU in Tukwila, Wash.; and $10.3 billion SchoolsFirst Federal Credit Union in Santa Ana, Calif.

But what about the little guys and mid-size credit unions? Do they keep a smaller share if a member withdraws funds from a CD before it matures?

Larger FIs tend to play hardball, according to Bankrate.com's survey, but organizations with less assets are often much more lenient to members who cash out early.

For example, at TLC Community Credit Union, the principal balance on CDs is protected and members only lose additional interest for early withdrawals, the credit union said.

“Even with the current low interest rates, we will not increase or alter our penalty policy on CDs,” said Mike Servoss, EVP at the $343 million TLC Community Credit Union in Adrian, Mich.

At credit unions that do keep a larger slice of the pie for early withdrawals, do members interested in CDs need more education about the risk of possibly losing more than just interest earned?

When discussing penalties, it's important that members completely understand the terms and conditions of the product, said NCUA Public Affairs Specialist John Fairbanks.

“We think it's important to clarify the point about institutions using principal to pay early withdrawal penalties,” Fairbanks said. “This, to our knowledge, only occurs when a penalty ensues that exceeds the available accrued interest.

“So it's not really a matter of the principal being confiscated. In exchange for generally receiving a guaranteed higher rate of return, a member who buys a share certificate agrees to certain terms, usually including early withdrawal penalties, which are outlined in the disclosures for the certificate being purchased.”

Fairbanks said most credit unions seem to be doing a good job of explaining penalties to members.

“We don't believe this is a problem area in credit unions, in particular because they have historically offered consumer-friendly share certificates,” he said. “A word to the wise for consumers is important though.”

To avoid any confusion, the NCUA and Bankrate.com urged credit unions to advise members to read terms carefully and ask questions about anything they are not confident they completely understand.

Members also should be encouraged to make certain they can live without the money for the required amount of time before opening a CD that carries an early withdrawal penalty, McBride said.

As an alternative, members could opt for a shorter maturity or a CD that contains a liquid or no penalty feature, but the price for that flexibility could be a smaller yield, he said.

“Investors look to CDs for a return of their money … early withdrawal penalties threaten the return of the investment they're trying to protect,” McBride added.