Many don’t even manage to obtain a contract and are also paid under the minimum rate. Some immigrants work for 4 euro an hour. Employment law is tough for the employer (in principle). A friend sacked a Spanish worker (he had been taking drugs on the premises). Because she did not follow the correct procedure she was ordered to pay him one years salary.
The majority of workers are on 6 month contracts. Some businesses have two companies and the workers they want to keep are transfered to the second one after 6 months and then back again. They can work there for years and never aquire any rights.
I sometimes read a Spanish ex-pat blog. Some interesting comments on their comparison to working in Spain to other countries. One from Málaga thinks he has found paradise in London as the working conditions etc are so much better.
To sum up I would say the employment laws here only work for some, bit like bank guarantees really 😆