Information about thousands of staff at a Devon council, including bank account details, have gone missing.
The council's chief executive has apologised to staff
Records of 6,500 Torbay Council workers were on a CD posted to the Audit Commission, but which did not arrive.
A second disc, containing staff names, addresses, salary and banking details, was then sent, and also did not arrive.
The council's chief executive admitted the CDs were sent in the general post. An officer has been suspended and an investigation is under way.
Elizabeth Raikes told the BBC the correct procedures had not been followed.
"Clearly it's most undesirable it should have happened a second time," she said.
"I really want to get to the bottom of this because I need to restore the trust of our council employees and, indeed, the public of Torbay."
But the chief executive said she had no intention of resigning over the matter.
The council said the matter came first came to light last December when the Audit Commission reported the data had not been received.
Ms Raikes said extensive inquiries had been made to try to recover the data.
Royal Mail said more than a million items were handled every day in the Torbay area and it was not possible to track items of post which had not been recorded or sent by special delivery.
A statement said: "In the vast majority of cases mail goes missing due to circumstances beyond our control - poor, incomplete or inaccurate addressing being among the principal reasons.
"As a general rule we recommend that anyone sending important or time-critical information should use our special delivery service, which is a guaranteed next-day service enabling us to tack and trace individual items."
One council employee said she was absolutely shocked when she received a letter from the council.
"I was probably more annoyed, though," she said. "These are my details and God knows who's got them now. It's worrying."
She said she had spent much of the morning on the telephone to her branch of Lloyds Bank.
"I am slightly more reassured now the bank's told me people will need extra information before any details will be given out," she said.
A union spokesman said legal advice was being sought over the matter.
Ken Terry, of Unison, said: "I am horrified that such an incident could occur."
A telephone hotline has been set up and workers are being advised to check credit references and bank statements.