Lancaster and Fleetwood MP Cat Smith made the claim in a letter to Amber Rudd, secretary of state for work and pensions.
Ms Smith wrote: "I have just finished my weekly advice surgery in Fleetwood. During the surgery, 40 per cent of attendees have threatened to kill themselves due to issues with their social security.
"It is clear that the current system is not working at all. In 2019, as one of the richest societies in the world, people should not be coming to my advice surgery completely despondent and at the end of the line. It is not good enough.
"I would implore you urgently to address and reform the fundamental flaws in the Universal Credit system.
"people should not be left with no money for weeks on end."
Universal Credit is a means-tested benefit for people of working-age who are on a low income.
It replaces six existing means-tested benefits and is paid monthly. The changes to the benefits system have come in for criticism after claimants were left for up to six weeks waiting for payments.