Taxing: Why ATO working day ends at 4.51pm

AUSTRALIAN Tax Office staff have finished work at 4.51pm for years but now there are plans to bring them into line with the rest of us - and staff aren't happy.

The proposal to finish at 5pm would add an extra 4.5 working days a year.

While many staff work beyond 5pm - particularly those highly paid ones with extra responsibilities, the ATO conditions are said to be among the most generous in the country.

Documents obtained by the ABC under freedom of information laws reveal the push to extend working hours to 5:00pm proved "highly contentious" and was ultimately dropped to ease concerns.

Bringing the ATO in line with the rest of Australia would improve productivity by 2%.

But negotiations with the unions have now dragged into a third year.

"Of all the changes proposed in the enterprise agreement (EA) package, this was the one you told us you disliked the most," ATO briefing packs reveal.

"It was clear from your feedback that this had to go and I think it goes a long way to demonstrating that we're genuine about getting an EA in place for the next three years."