An MP will attempt to introduce a law to end unpaid trial periods for workers following public anger at some of the worst examples of exploitation.

The SNP’s Stewart McDonald, who represents Glasgow South, said: “It’s an issue I feel very strongly about and hope to secure support from other parties to end this unscrupulous practice that exploits so many.”

Explaining his reasons on social media, he cited the case of two Glasgow cafés who were allegedly asking potential staff to undertake 40 hours of unpaid work before they could be considered for employment.

After more than 13,000 people signed the petition objecting to the practice of two Mooboo Bubble cafes, Mr McDonald took up the case, writing an open letter to the Treasury.

He said in his letter: “I’m concerned this unpaid 40 hour trial is in breach of the national minimum wage definition.”

Dozens of people responded to Mr McDonald’s tweet about his proposed change to the law, many sharing similar stories of unpaid work trials.

One woman said: “About time too, in the hospitality/events industry you are expected to work for free constantly whether it’s trials or volunteer work.”

Some asked for the law to be widened to cover unpaid internships as well.

Jobcentre Plus runs an official Work Trial programme for the unemployed, where the period of unpaid work can last up to 30 days if agreed, and the person on trial can continue to receive benefits.

The Government’s website lists the benefits of its official work trials, telling potential employers: “It’s risk free – you can try the person out before making a final decision” and “there are no wage costs – people continue to get their benefits.”

Outside of the official scheme, informal work trials lasting up to a full day are common – particularly in the hospitality industry – but the Advisory, Conciliation and Arbitration Service (Acas), says the law isn’t clear how long a trial has to be before it becomes work for which a person should be paid.

Unions have raised concerns about the potential exploitation of people through work trials.