The Government has talked out a Bill which sought to ban unpaid trial shifts, amid concerns that people with learning disabilities are more likely to "fall victim" to the practice.
The SNP's Stewart McDonald, moving his Unpaid Trial Work Periods (Prohibition) Bill at second reading, said it was often people who "don't know their rights and can't stand up for them" who are exploited.
The Glasgow South MP said current legislation was "insufficient" in dealing with unpaid trial shifts.
But business minister Andrew Griffiths said that while he was "very keen" to work with Mr McDonald to address the issues, he did not think there was a need for more regulation.
"I think that there is a very clear way in which we can do this without the need for further regulation because what is clear is that the law is already very, very clear on this point," he explained as he talked out the bill.
READ MORE: MSPs attack firms for unpaid trial shifts
Fellow SNP MP Neil Gray said the "greatest tragedy" was that most often those "exploited" have "learning disabilities" and "are desperate for work and see these as their only opportunity and that is one of the key reasons why this Bill must pass".
Mr McDonald replied: "Too often that is what happens and the people who fall victim to this are those who either don't know their rights and can't stand up for them, or those who are unwilling to challenge employers on their rights because they are in fear of losing their job.
"This practice hits the lowest paid and the lowest skilled in our economy and this is a Bill to protect the lowest paid and the lowest skilled."
He said he would never again shop in bargain store B&M after being "horrified" to learn that a young man with autism had been "stacking shelves for three or four days" for them before being sent away with no pay.
And Mr McDonald told the Commons that supermarket chain Aldi advertised for 150 unpaid trial shifts when opening a new store in the north east of Scotland.
"This cannot go on and today we have a chance to end it," he said.
Mr McDonald claimed he found an advert on website W4MP for an unpaid internship from 2012 in the office of Mr Griffiths.
The minister said he had "never, ever had an unpaid internship" in his office and later clarified, via a point of order, that the position had been advertised but not filled.
Mr Griffiths, amid questions as to whether the Bill would apply to work experience or taster sessions in a work environment, intervened to say: "As it's drafted, this Bill would exclude those kinds of things - anything from making the coffee briefly would be outlawed.
"The Bill sets the threshold at zero, so any moment spent working would be caught up within this Bill."
Shadow business minister Alan Whitehead replied: "I'm not sure the minister, if I may say so, has correctly put across the idea of what working is. Various things which don't actually constitute work but constitute other things not related to work would not be covered by this particular Bill.
"Where there is clear work being undertaken, and that work is recognised in the normal sense of the word, then it would be covered by the Bill."
Mr Griffiths added: "Those kind of trials, those kinds of tests would not be covered by the national minimum wage so payment would not be applicable anyway."
Mr Whitehead earlier welcomed the Bill, adding it was about the principle of a "fair day's pay for a fair day's work".