The remit comprises media relations work for the firm, which supplies high bandwidth data, internet and voice services to firms across Europe.
The account has been held since last year by Burson-Marsteller, but Colt UK marketing services manager Graham Cook confirmed a pitch was underway.
Cook has sent what he termed a 'screening questionnaire' to 12 agencies, which, he said, range from large generalist agencies to tech specialist PR firms.
B-M, which has worked for Colt UK for around 18 months, has been invited to repitch and Cook stressed he was not unhappy with that agency's work.
'The decision to repitch is based on different factors. Our new contracts will move away from traditional retainer arrangements towards results-based performance,' he said.
Around six agencies will be culled from Cook's list on the basis of their responses, leaving the remainder to submit a tender for the work.
Cook said he expects to meet 'two or three' agencies before deciding which agency to appoint. The selected agency will start work on 1 January and will handle media relations with the national, regional, trade as well as technical press.
Colt's main rivals in the UK are BT, Cable & Wireless and Energis. Founded in 1992, the company operates in 32 European cities in 13 countries.
The group is majority-owned by US investor Fidelity Investments and employs around 5,000 staff across the continent.
There has been media speculation in the past month that Fidelity could be planning to sell the firm, with BT emerging as a possible buyer.