But the plan already faces opposition, with one workplace union ridiculing the proposal as bosses planning to email their workers "back to health".

The ATO says it will trial a scheme where each of its 20,000 workers will get a regular email reminding them of their recent absenteeism record and how it compares against their colleagues.

The ATO has been encouraging its managers for several years to tackle the agency's sickie problem, with the Tax Office still among the worst performers of the big Commonwealth departments.

Despite being among only a small number of agencies to improve their rates of unscheduled absence in recent years, the ATO's workers were still clocking up more than three weeks, on average, of not showing up to work in the 2013-2014 financial year.

But efforts to combat the problem have met with friction.

Union opposition shot down an initiative in December 2014 which rewarded good attendance at a Queensland call centre with a chance to win scratch cards from under the office Christmas tree.

The Australian Services Union argued the plan discriminated against tax officials who did not show up to work.

In a briefing to unions this week, one of the ATO's human resources bosses, Margaret Jamison, said she wanted to trial the new system so the agency could better understand "voluntary and avoidable absences".

"The ATO is committed to supporting appropriate leave usage, as per enterprise agreement provisions, to assist employees to manage their general health and well-being, caring responsibilities, and family emergencies," Ms Jamison said.

"Like most APS agencies, however, we are currently working on a range of initiatives to address high levels of workplace absence."

Ms Jamison said the proposed emails would bring employees up-to-date on a number of their workplace entitlements.

"Current considerations for inclusion are leave days during the past month, past 12 months, number of separate leave events during the past 12 months … visual 12 month calendar of leave taken, and a comparison of leave levels to the average in their business line."

Despite early testing on a small group of volunteers, Ms Jamison said the plans were in the development phase and no definite decision had been made on the trial.

But the ASU is in no doubt that it is unhappy with the idea, with union official Jeff Lapidos dismissing it as a "thought bubble".

"The ATO has become obsessed with the notion that employees are taking sick leave just for the fun of it," he said.

"Its position seems to be if only employees could be 'engaged' with their work, then the use of personal leave would plummet.

"The ASU has told the ATO over the years that much sick leave use is because of how the ATO is managed, with insufficient regard for the individual needs of employees."