It also claims more than a third of employers in Scotland admit they do not provide training, and that two fifths of the workforce received no training at all last year.
With more than 1,500 jobs in manufacturing lost in Scotland this year, the report says the remaining 200,000 still working in the sector need training to ensure existing skills are not lost from the economy.
The report calls for a new Scottish skills strategy to create a list of agreed priorities, roles and responsibilities - particularly on investment.
The STUC believes unions are "uniquely positioned" to improve skills and learning in the workforce.
In another report published last week, it noted: "Last year alone, over 15,000 workers received personal information, advice and guidance on learning due to the Scottish Union Learning Fund. Because of the fund, 13,000 union members, mostly non-traditional learners, have completed a course."
The congress wants to see the establishment of a Scottish Union Academy which would help unions expand learning services further.
Photograph: Ashley CoombesEpicscotland