Reason for the 55688 Monopoly at Hsinchu HSR Station?

I take a taxi quite often from the Hsinchu HSR Station, but for the last few months around the “holiday season” there could be quite a line, up to 30 minutes if it was raining. But I noticed there is a little gate which I am assuming they have some sort of surcharge to pick people up, and it’s always “55688” Taxis. What is the reason for monopoly, and what happens if I just jump in a non 55688 cab after it drops somebody off at the station?

I notice more than one HSR station seem to have an odd taxi arrangement going on.

Taichung HSR Station has two taxi companies when you come down the escalator, one on the left and one on the right, with both touting for your business! Apart from that strange arrangement it’s actually very quick and convenient.