A Scottish MP has stepped up his campaign to outlaw unpaid "trial shifts" which he said have become common in the UK.
Stewart McDonald, who represents Glasgow South, has written to every MP asking them to back a Private Members' Bill.
The proposed law would end the practice of people being asked to work without pay and with no guarantee of a job.
The bill has the support of Scottish trade union body, the STUC.
Mr McDonald said some shops, bars and restaurants would be using unpaid trial shifts to cover staff shortages over the holiday period.
He said: "Unpaid trial shifts are common practice across the UK.
"However, they are exploitative and take unfair advantage of people genuinely seeking work.
"Over the Christmas period, it is increasingly likely you'll be served in a shop or a restaurant by someone working an unpaid trial shift."
Mr McDonald, an SNP representative, added: "The Private Member's Bill I have brought forward has received the support of the STUC, NUS, and the Better than Zero campaign - who are to be commended for the excellent work they have done in documenting and challenging exploitative work practices in different industries."