The Chancellor should equalise the limits for cash Isas and stocks and shares Isas in this year's Budget, Nationwide says.
Nationwide's chief executive, Graham Beale, has written to George Osborne to highlight the importance the society places on supporting the savings aspirations of the country's consumers and the role Isas can play.
The building society also called for a review of Stamp Duty when the Government announces the latest spending plans on March 19.
In the letter, Nationwide reiterated requests to improve the Isa regime, providing simplicity and support for savers.
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Mr Beale said he wanted to see:
• An increase in the annual deposit limit for cash Isas to equal the limit for stocks and shares Isas – to both reduce confusion and encourage new savers. Currently, account holders can only save up to a maximum of £5,760 in a cash Isa, but up to £11,520 in a stocks and shares Isa
• Transfers allowed from stocks and shares Isas into cash Isas – to provide greater flexibility, particularly for those wishing to have easier access to their savings, such as older people and those approaching retirement.
• First time homebuyers to be enabled to save even more in a tax-efficient cash Isa account towards a deposit for their home.
Mr Beale said: "The Chancellor holds the power to reinvigorate the UK's savings culture in his hands.
"In the current climate of depressed rates, the need for a flexible and supportive savings regime has arguably never been greater.
"As an industry we need to demonstrate support for hard pressed savers, and making Isas more straightforward may encourage more people to make the most of their tax-efficient Isa allowance."
Last year, Nationwide research showed that 66% of Isa savers wanted cash Isa limits brought into line with higher equity limits for all savers, and that 31% found the differences between the two limits confusing.
HMRC data suggests that in 2012/13 approximately four cash Isas were taken out for every one stocks and shares Isa, suggesting that the majority of savers want the greater flexibility that cash Isas allow to access their money.
He also encouraged the Chancellor to reform the current 'slab' structure of Stamp Duty Land Tax.