Employers and Manufacturers Association (EMA) chief executive Alasdair Thompson today unreservedly apologised for his comments that sparked hate mail and calls for his resignation.

Mr Thompson yesterday told NZPA he did not intend to resign of his remarks, after he yesterday implied women got paid less "because once a month they have sick problems".

"Not all women, but some do, they have children they have to take time off to go home and take leave."

He had made his remarks during a NewstalkZB interview on Green Party MP Catherine Delahunty's bill seeking to require employers to record the gender of their employees along with pay levels.

There were immediate calls for him to resign. He received hate mail and trended on social networking website Twitter.

Mr Thompson earlier apologised for causing offence, but stood by his overall argument.

He today issued an "unreserved and unqualified apology" for his comments and behaviour.

"I apologise for my poor choice of words and bad judgment during the discussion about gender and productivity in the workplace," Mr Thompson said.

He had started out with genuine concern for the problems women face in the workplace but that soon disintegrated into "facile observations that did a disservice to what is a very serious matter".

"I raised issues that were misplaced and irrelevant to the discussion," he said.

"I realise my remarks offended many people. I have personally always supported equal pay for equal work, equal opportunity, respect and courtesy for both women and men in the workplace."

Mr Thompson said the EMA unquestionably believed in equal pay and that gender played no part in people's productivity.

"Although this experience has been very painful to me, it has also served as a valuable lesson -- one I shall never forget."

The Pay Equity Challenge Coalition today issued a statement saying Mr Thompson’s comments showed the need for legal protection against discrimination.

Yesterday Women's Affairs Minister Hekia Parata and other females MPs and unionists condemned his initial comments.