Lecturers at the London college are being deducted half a day's pay every time they refuse to co-operate with observations, which they argue are not supportive, are inconsistent and are a source of extra work and stress.
The University and College Union (UCU) congress voted to ensure that members were financially compensated for the deductions as a mark of support.
Westminster Kingsway delegate Peter Green said: "Many people didn't think a boycott would be feasible, that it would be too difficult to monitor. But the reason we've sustained this boycott is because it's the most popular action we've ever taken.
"You can say we're not going to do the extra paperwork, we're not going to be subjected to arbitrary classification. I would urge any branch in a similar position to take the same action."
Staff at the college's catering department, a centre of vocational excellence, have declined to take part in the boycott, however.
UCU members at the congress passed a series of motions condemning the regime of inspections and internal, graded lesson observations, which they said had no beneficial effect on teaching.
They called for the union to establish agreed guidelines with the Association of Colleges for the conduct of lesson observations, which would include a ban on unannounced visits.