Leaders of the main unionist parties in Scotland are preparing to issue a joint statement promising more power for Holyrood, the BBC understands.
Johann Lamont, Willie Rennie and Ruth Davidson could share a platform as early as next week.
Sources say it will not be a formal pact, but will indicate a ''direction of travel'' from Labour, the Liberal Democrats and the Conservatives.
The Scottish government said only independence guaranteed more powers.
Each of the main pro-Union parties have separately promised to devolve more power to Holyrood if there is a "No" vote in September's independence referendum.
Earlier this month, the Conservatives published the findings of their fiscal commission, which recommended Scotland be able to set its own income tax bands and rates while the tax free allowance remained reserved to Westminster.
Labour has said it would devolve three quarters of the 20p tax rate and give Holyrood control over housing benefits.
The Lib Dems want Holyrood to raise 50% of the money it spends and have control over income, capital gains and inheritance tax.
While the parties disagree on detail, sources say they are now sufficiently close to share a platform at which they will commit themselves to greater devolution.