The Mental Health Alliance has argued that more must be done to ensure the rights of mentally ill people are protected as controversial legislation progresses through parliament.
Opposition and non-aligned peers have tabled several amendments to the mental health bill, which enters its report stage in the Lords today.
Previous attempts to change the Mental Health Act 1983 were scrapped following opposition in the mental health and medical sectors.
"People should not be detained under mental health law unless there is a likelihood treatment will help them," said Mental Health Alliance chairman Andy Bell.
"The government has gone some way to acknowledging this by stating that treatment should have the purpose of helping the person."
However, he warned the bill still contained "too many new powers to detain people and use compulsion outside hospital without adequate safeguards".
"Until we see changes to the proposed community treatment orders and the broad definition of mental disorder, the bill remains unacceptable," he added.
Laws with "clear principles" were needed, Mr Bell stressed, highlighting that detainees should have advocacy rights and a right to choose which relatives are consulted.
The Mental Health Alliance is an umbrella organisation representing 78 organisations, including psychiatrists, lawyers, psychologists and carers' associations, with the main aim of securing better mental health legislation.