Labour said new analysis of figures from Colleges Scotland showed 73.7 million hours were provided in 2012-13, a drop of 9.7 million hours from the total in 2009-10.
Education spokeswoman Kezia Dugdale accused the Scottish Government of having "targeted our colleges for cuts" and said the consequence of this was "learners being denied opportunities".
But a spokesman for Education Secretary Michael Russell insisted Labour was "deliberately misrepresenting" the figures.
Labour commented after education body Colleges Scotland published a series of key facts about the sector.
According to the figures, student numbers have dropped by more than 100,000 in the past three years, while staff numbers have dropped by almost 7,000. The statistics follow a series of college mergers that created 10 larger regionalised institutions as part of the Scottish Government's wider post-16 education reforms.
The SNP administration argued the mergers would deliver efficiency savings and combine teaching expertise, but Scottish Labour said the latest figures are evidence of a "disgraceful record" on education.
Ms Dugdale said: "The SNP has targeted our colleges for cuts and the consequence has been young people and second-chance learners being denied opportunities to get on in life."
The statistics undermine claims by the Yes campaign that September's referendum on Scottish independence is focused on young people, she said.