Two Glasgow cafes who are accused of asking workers to do unpaid work before being considered for a job are facing widespread criticism from politicians and activist groups.

A petition calling for an enquiry into the Mooboo Bubble Tea stores in Buchanan Galleries and the St Enoch Centres has now surpassed 13,000 signatures and MP Stewart McDonald has written an open letter to HMRC about the issue.

It is alleged that Mooboo have asked staff to undertake 40 hours of unpaid work before they can be considered for employment, with no guarantee of a job if the trial is completed.

Mr McDonald, representative for Glasgow South, said: “I’m concerned this unpaid 40 hour trial is in breach of the national minimum wage definition.

“I’m asking that HMRC officials investigate this matter thoroughly to ensure that prospective employees are not being exploited and to send a strong message that this kind of behaviour is completely unacceptable.”

In his letter, the SNP MP also mentioned that the company had blocked him from communicating with the company on social media, along with a number of others who had asked about their working practices.

Mooboo have since been contacted Mr McDonald stating that their programme is for training purposes and it is an important step in properly preparing staff.

The politician will now speak with other MPs in the House of Commons with Mooboo franchises in their constituencies.

The issues first came to light at the end of last week as campaign group Better than Zero launched a petition after they had received reports of the unpaid work.

Emails to prospective staff at the two Glasgow stores show that 40 hours of training were needed but did not mean that was employment was assured.

The appeal is now on its way to meeting its 15,000 signature target.

Bryan Simpson, Glasgow branch organiser for Better than Zero, said: “Currently there is no hard and fast legislation on shadow shifts which means that there is nobody policing what is going on.

“We have had reports from former staff, who do not want to be named, that they were left alone for periods during their trial shifts.

“We are a grassroots organisation but it is good to have a voice like Stewart McDonald supporting us at that kind of level.

“Maybe this is just one manager but we are getting more reports coming in from across the country so it seems that this is being replicated elsewhere.”

Workers from stores in Liverpool and London have also been in touch with the Better than Zero campaign to let them know of similar experiences elsewhere.

Mooboo have been operating in Glasgow since June 2014 with both sites run by the same franchise.

When approached about the claims by the Evening Times Mooboo’s management chose not to comment.