David Cameron has said the government will bring forward proposals for a transferable tax allowance for married couples and civil partners “shortly”.
The BBC understands it will happen some time in the autumn.
Mr Cameron has been under pressure from Tory backbenchers to honour a plan for tax breaks made in the 2010 manifesto.
Labour opposes the idea and the Lib Dems were given a specific opt-out in the coalition agreement which means they do not have to support it.
Under plans being considered, wives and husbands who do not work and pay no income tax would be able to transfer part of their annual tax-free allowance to their spouse if their partner earns less than the higher rate of tax, which currently kicks in for people earning £41,451 or more.
In 2010, the Tories said it would make four million married couples and civil partners £150 a year better off.