According to the certificate terms listed under the rate table:
Additional deposits are permitted for Add-On Certificates only. You may make additional deposits to an Add-On Certificate at any time. There is no minimum amount requirement for additional deposits.
There doesn't seem to any limit on the additional deposits. This can be a very useful feature when there's the potential that rates will remain low or continue to fall. When your other CDs mature, you always have the option to add on to this CD. If rates rise, you can choose other options.
The credit union also has a new-member promotion in which you can receive $100 for joining the credit union and opening a checking account with direct deposit. The checking account must be opened by 5/31/08. A minimum direct deposit of $100 must be received by 7/15/08 to obtain the bonus.
My first post on this credit union was last November when they were offering a 6% 18-month CD.
When I first posted on this credit union in November, it appeared anyone could qualify by joining the National Wildlife Federation. However, the credit union's board changed this eligibility criteria to only include employees of National Wildlife Federation. So there's no longer an easy way to qualify for credit union membership. The credit union's field of membership is primarily limited to Select Employee Groups. Please see their Who Can Join page for more details. There is a long list of member companies. Membership requires a minimum deposit of $5 into your share savings account.
Branches are located in the Virginia cities of Chantilly, Herndon and Vienna. The credit union is federally insured by the NCUA (Charter # 5500). It's a large credit union with $1.50 billion in assets and 92,177 members.
Thanks to the reader who emailed news of these add-on CDs.