Thousands of public servants at the Commonwealth's largest department aim to force their bosses to the negotiating table; with a mass lunch break.

Officials at the Department of Human Services, fed up with what they say is a lack of appetite by their bosses for wage talks, will protest by taking co-ordinated lunch breaks on Thursday, February 19, at 1pm, 2pm and 3pm.

About 14,000 union members at the giant department will turn the heat up on their bosses even further by setting their email accounts to auto-reply sending back a message authorised by the Community and Public Sector Union backing their workplace claims.

The department's management confirmed on Wednesday that it had pointedly been excluded from the invitation with DHS's general manager of communication Hank Jongen saying the mass lunch date was news to him.

"We are yet to receive formal notice of the proposed industrial action," Mr Jongen said.

The news comes as the Australian Taxation Office defends its pay offer of less than $7 a week - conditional on extra working hours - to the vast majority of its 23,000 strong workforce.

The Tax Office says the proposal is "balanced and affordable" and that its workers have enjoyed the shortest working hours in the Australian Public Service for years.

Human Services' 35,000 workers have been waiting since mid-2014 for the department to make them a pay offer after an attempt to hold a ballot for a below-inflation deal collapsed in July with management, unions and even Public Service Minister Eric Abetz  trading recriminations.

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Now the CPSU has asked members for another day of action, following a low-key campaign of industrial action in late 2014, but not too much action.

"All union members will be asked to take co-ordinated lunch breaks at midday, 1pm and 3pm," according to a bulletin sent out to union members.

"All members will be asked to put in place an automated email response to all internal emails received on the day that will include a campaign and join message."

Human Services management has been contacted for comment.

Meantime, ATO management says its workers have enjoyed some of the lowest working hours in the public service.

Unions reacted with outrage on Tuesday to the ATO's pay offer, branding it "miserly, nasty" and an effective pay-cut.

But in a statement issued late on Tuesday night, the agency's media department says staff are relaxed about the loss of an annual $300 health and welfare payments and other "outdated" conditions.

"This pay offer is affordable and is fully offset by productivity," the statement said.

"The main productivity measure involves increasing the standard working day by 9 minutes to 7 hours 30 minutes from 7.21 which is one of the lowest working days of any APS agencies.

"In addition the offer seeks to remove the health and well-being allowance which staff have indicated their willingness to consider, and a range of other out-dated allowances

"It is a balanced, affordable offer."