Widespread discrimination against mothers in the workplace has been uncovered by a new survey that the extent of career damage caused by having a child.

Three-quarters of the 1000 mothers questioned in the survey published today said they had found it harder to progress their careers after starting a family. Six out of 10 mothers felt they were less employable after giving birth.

Almost half told the Mumsnet organisation they were made to feel guilty for getting pregnant. In some case their managers told them they were "disappointed" with them, a clear breach of human relations policies.

Others said their job had been given to another employee, without consultation, while they were on maternity leave. The problems continued on return to work with nearly half (46%) claiming they were made to feel guilty for leaving on time to collect their children.

Justine Roberts, Mumsnet's chief executive, said: "While we have legislation designed to protect women against discrimination in the workplace it's clear that in many cases companies are simply not following the rules.

"With over half of mums saying they felt less employable and three-quarters saying it was harder to progress in their career since having children, it's clear there's still lots of work to be done to ensure family friendly practices are commonplace."

Eileen Dinning, the former chairwoman of the Scottish Trade Union Convention's Women's Committee, said the findings of the survey reflected many women's experiences in the workplace.

"Employers commonly breach the equalities legislation but many women are so scared of losing their jobs that they do not act upon this," Ms Dinning said. "Flexible working arrangements are the key but the current rules are not fit for purpose."

The survey found discrimination began at the announcement of pregnancy, with 17% of mothers saying their line manager was not supportive. One mother said: "I was told no-one wanted to see a pregnant woman waddling around the restaurant."

Discrimination continued after maternity leave with one in four saying they felt their job was under threat. One mother said: "My job was given to someone else while I was on maternity leave; I was not made aware until I had my return-to-work interview."

Asked what employers could do to be more family friendly, the most popular policy was flexible working, with 28% of respondents favouring this option. Next most popular was emergency childcare provision with 15% support.