The Illegal Migration Bill risks breaching international obligations to protect human rights and exposing people to serious harm, the Equality and Human Rights Commission said.
The body issued the warning ahead of the Commons report stage of the proposed legislation on Tuesday.
The Bill, which would change the law to make it clear people arriving in the UK illegally will not be able to remain in the country, has prompted criticism from opponents who have dismissed it as unworkable.
But right-wing Tory MPs said the legislation does not go far enough, with some calling for ministers to take the UK out of the European Convention on Human Rights (ECHR) to gain tighter border controls.
Others on the liberal wing of the party want to see the Prime Minister commit to establishing safe routes through which asylum seekers can come to Britain.
The Commission said it “remains seriously concerned that the Bill risks placing the UK in breach of its international legal obligations to protect human rights and exposing people to serious harm”, adding: “Provisions providing for the detention of children and pregnant women and removing protections for victims of trafficking and modern slavery are particularly worrying.
“Effective, rights-compliant action is needed to ensure that more lives are not lost on dangerous Channel crossings. We welcome the Government’s commitment to increase safe, regular routes to the UK for those in need of asylum and recommend these are brought forward alongside the Bill.”
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