Have employers ever been able to require childlessness as a condition of employment?

I read a personal history several years ago in which a woman was interviewed for a professional position in the early 70s and was told in the interview that she would have to commit to remaining childless for a certain time as a condition of employment. At least I think that’s how I remember it. Was this ever legal in the US (or your country)?

I think this might currently be allowed for certain jobs that involve exposure to toxic chemicals or radiation, but this wasn’t that kind of job—the employer just wanted a guarantee that the woman wouldn’t leave the job to have a child after the employer had invested time and money in training her. I’m fuzzy on the details of the guarantee, but I think it might have gone as far as asking the woman to state that she would use birth control and get an abortion if necessary.