Opposition parties in Japan are pressing Health Minister Hakuo Yanagisawa to step down for calling women "birth-giving machines".
Yanagisawa: 'Realises he has offended women and men'
The Democratic Party and two smaller parties are threatening to boycott budget hearings in parliament if Mr Yanagisawa, 71, does not quit.
The Democratic Party called the remarks inexcusable and said they violated women's human rights.
Mr Yanagisawa has apologised for his comments, which he made at the weekend.
The gaffe has caused embarrassment to Prime Minister Shinzo Abe, whose popularity is slipping and who has already had one minister resign over political funding.
Mr Abe has rebuked the health minister for his remarks, but has dismissed calls for his resignation.
Tackling birth rate
Mr Yanagisawa had told a local political meeting "Because the number of birth-giving machines and devices is fixed, all we can ask for is for them to do their best per head."
Japanese children are fewer and further between
On Monday he told parliament he would "make every effort in the Abe government to work out measures to solve the problem of the low birth-rate."
Prime Minister Abe has pledged to bring in policies that will tackle the falling birth rate.
Japan has the world's highest ratio of elderly to young people.
The trend raises serious concerns about the country's future economic growth and how it can fund its pensions.
It also has forced Japan to question its attitude to immigration.