It is also on the hunt for an agency to promote its Quarterly Savings Survey - an analysis of the way the public save and invest.
The savings and investments provider has used The Wrigglesworth Consultancy for three years and is tendering its account as part of a statutory review.
NSI wants to be seen as the most trusted savings and investments body in the UK.
Ogilvy Bulletin's broadcast media relations account is not affected.
NSI is currently promoting its Index-linked Saving Certificates and raising awareness of how to save with tax-free returns.
It is targeting personal finance, national and regional press and consumer titles.