The boss of the federal government's largest department has apologised to her workforce after some of them were depicted as rodents, then toilet paper on an internal online platform.

Department of Human Services secretary Kathryn Campbell wrote to her 34,000 public servants on Wednesday after a week of public relations disasters, saying she was sorry for any offence caused in the ranks by the rats and loo paper affair.

Ms Campbell, whose department runs Centrelink, Medicare and the Child Support Agency, also addressed the coverage of the scathing report into waiting times on the welfare agency's phone lines, savaged in a federal government audit.

DHS public servants were furious earlier this month after discovering the icon depicting workers taking protected industrial action on an internal human resources platform, was what they said was a rat.

When the icon, which departmental bosses insisted was a mouse, not a rat, was changed to a roll of toilet paper, departmental insiders were further appalled.

Eventually it was decided that workers taking stop-work action should be represented by the letter "p" on the system

Ms Campbell did not express a view in her all-staff email on the mouse or rat question, but said systems were now in place to ensure there would be no repeat of the debacle.

"I also wish to put on the record an apology for any offence taken by the selection of icons used in one of our Smart Centre scheduling tools," the secretary wrote.

"It was unintentional and processes have been established to identify such sensitivities into the future."

Ms Campbell also tackled the aftermath of the Auditor-General's report which found tens of millions of callers to Centrelink failing to get through and ballooning waiting times for those who did manage to get an answer.

"I am keen to address recent criticism in the media about us losing sight of our customers," Ms Campbell said.

"Nothing could be further from the truth.

"I want to reassure you the recent criticism of our call wait times is no reflection on the outstanding work of our Smart Centre staff.

"I know those of you working in this complex environment have a passionate commitment to delivering excellent service.

"It does, however, reinforce why we must continue to transform the way we deliver our payments and services."

The secretary also denied reports that her senior executives had been spared the pain visited on the rank-and-file in the department in recent years.

"The number of SES officers in our department has reduced by over 18 per cent, compared with an overall staff reduction of just under eight per cent since 2011.

"I can also confirm the SES have not received an increase in their pay since 2013."