Treasury considered dividend imputation reform in the lead up to Treasurer Scott Morrison's last budget, creating a dossier entitled "Tax Policy - Dividend Imputation" more than a year before Labor announced it would target the tax refunds of more than one million Australians on Tuesday.

The confidential file itemised in a list required to be disclosed by departments as part of freedom of information requirements was opened by Treasury in the first-half of last year.

Fairfax Media understands Treasury has been examining withholding dividend cheques from non-taxpaying shareholders ahead of this year's May budget.

Investigating potential savings needed to fund budget initiatives such as personal income tax cuts is normal practice in the pre-budget period.