Asylum seekers on the UK's only migrant barge live in "small, cramped cabins" that harm their mental health, senior MPs have said.
The Home Affairs Committee said it was "disheartened" by its site visit to the Bibby Stockholm moored at Portland in Dorset.
In a letter to the Home Office, the MPs said the crowded conditions "could amount to human rights violations".
The government said barge residents' welfare was "of the utmost priority".
It comes after the government this week confirmed housing asylum claimants on the barge currently costs £120 per person per night, compared with the latest average of £140 per person per night in hotels.
Home Affairs Select Committee chairwoman Dame Diana Johnson has written to the Home Office following the committee's visit.
She said: "Many individuals having to share small, cramped cabins (originally designed for one person), often with people (up to six) they do not know (some of whom spoke a different language to them).
"These crowded conditions were clearly contributing to a decline in mental health for some of the residents, and they could amount to violations of the human rights of asylum seekers."
The Labour MP said the committee also found there was "very limited" access to religious services for Muslims, with one asylum seeker telling a member of the delegation they had had thoughts of suicide as a result of having to reside on the barge.
An Albanian asylum seeker, Leonard Farruku, 27 asylum seeker, is believed to have taken his own life on board the Bibby Stockholm barge in December.
The committee said his death was "tragic" and members called on the Home Office to take "all suitable steps to ensure mental health support is available".
It also complained of "discrepancies" between the accounts of officials and asylum seekers themselves, noting MPs received "inconsistent" information regarding access to GP services for those onboard.
The vessel, which can house up to 500 men, first came into use in August as part of government plans to cut the cost of hotel accommodation for asylum seekers.
Home Secretary James Cleverly said he is "totally confident" the Bibby Stockholm meets all legal requirements when he was grilled by the same committee this week.
"We take both the physical and the mental health of the people who are in the asylum estate very seriously," he added.
The Home Office said asylum seekers were screened to identify vulnerable individuals and ensure they are placed in suitable accommodation.
"There are rigorous safeguarding processes in place on the barge. Residents have access to health and social care services, including mental health support," it added.