The workers took the protest to the proposed home for the new Scottish police force as Tulliallan Police College prepared for a feast to mark the end of a training course.
The GMB union said it was linked to 20 workers launching an overtime ban at Tulliallan Castle, near Kincardine, in a pay row.
Staff, mainly women, employed by Sodexo, which provides cleaning, security, reception and catering services, are unhappy over the offer of a pay rise of 1%.
The GMB is claiming they should receive the Scottish Living Wage of £7.20 an hour as most are on a minimum rate of just £6.37.
Staff voiced concernes that Sodexo was to bus in workers from other units to cover the Command Course dinner attended by college top brass last night.
GMB Scotland's Richard Leonard said: "We are reluctantly mounting a picket.
"We have been left with no choice. We want to peacefully persuade these workers not to cross our official picket line and not to carry out work our members would normally do."
He said a Sodexo memo to staff read: "There will be new faces in the kitchen and service points" and that they should "assist them in learning the ropes".
"They are being asked to saw off the branch they are sitting on and they will not do it," he added.
Sodexo has refused to comment on the dispute.