John Park, who quit Holyrood to become a union official, has claimed trade unions would be fragmented north and south of the Border if Scotland leaves the UK.
He said Scottish employees would no longer be subject to UK laws on paid holiday and maternity pay if voters back independence next year.
The former Labour MSP, who now works as policy and strategy director for the Community trade union, also claimed the loss of a block of Labour MPs at Westminster would make Scottish workers more vulnerable.
Mr Park said: “The SNP are happy to talk about reducing red tape and low levels of business taxation post independence but they have nothing to say about issues such as maternity rights, the right to paid holidays and redundancy pay – workers in Scotland should be very worried about that.”
“Unions at UK level need to understand this isn’t just about Scotland – the inevitable fragmentation of the trade union movement and the removal of Scottish Labour MPs from Westminster post independence will undoubtedly weaken workers rights across the UK.”
However, the SNP’s John Wilson dismissed Mr Park’s claims and said that successive UK governments had eroded the employment rights of Scottish workers.
The MSP for Central Scotland said: “Workers should have no fears about employment rights following a Yes vote for independence.
“Any government elected in Scotland would ensure that workers rights are fully protected under the existing UK and European legislation.”