MPs on the environment audit committee have written to Amazon, Asos, Boohoo, PrettyLittleThing and Misguided amid concerns cheap clothing is being discarded causing mountains of waste.
The committee has heard "shocking" evidence that the buying practices of some online retailers maybe forcing some manufacturers to pay garment workers illegally low wages.
Concerns were also raised about the low-quality of some "fast fashion" garments and the excessive waste that this business model is generating.
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Mary Creagh, who chairs the environmental audit committee, said: "Low quality £5 dresses aimed at young people are said to be made by workers on illegally low wages and are discarded almost instantly, causing mountains of non-recycled waste to pile up.
"The committee heard shocking evidence this week in parliament that the buying practices of some online fashion retailers may be putting UK clothing manufacturers in a position where they can only afford to pay garment workers illegally low wages."
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"We want to know that they are fully compliant with employment law, that garments have a decent life-span, and that profit is not put before environmental damage."
The committee has previously heard from investigative reporters that the going rate for a garment worker in parts of Leicester is £3.50 to £4 an hour.