The Scottish Conservative Party said there were some 70,000 students studying so-called Stem subjects last year compared to 86,000 in 2007, when the SNP came to power.
It follows a policy decision by the Scottish Government to focus on full-time, rather than part-time courses.
That means overall teaching time has largely been protected, but fewer students are able to access courses.
The Scottish Government says full-time courses help the economy as students leave college with better qualifications.
Murdo Fraser, a Conservative MSP who obtained the figures through parliamentary questions, said the shift was damaging.
He said: "The SNP has constantly expressed its desire to re-industrialise the Scottish economy, but cutting places in these subjects is preventing this from ever happening."
A Scottish Government spokesman said: "The Scottish Government has maintained the level of FTE college numbers and we have ensured that colleges are delivering the same level of teaching provision compared to last year, despite significant cuts to our budget made by the Westminster Government."