DTZ, which has a history that stretches back to 1784, was the first real estate adviser to be listed on the London Stock Exchange in 1987 and currently has a worldwide presence in 140 cities across 42 countries.
The commercial property specialist has used Spada to support its corporate PR, media relations and issues management since its acquisition of Donaldsons in 2008, which Spada had advised since 2004.
Property and financial services specialist Spada is understood to have declined to repitch for the account.
A spokeswoman for DTZ confirmed a pitch process was under way, but declined to comment further.
A four-way shortlist is understood to have been drawn up, consisting of agencies with a wider agency offering and experience.
One source suggested the pitch reflected DTZ's acknowledgement that it needed to expand its comms offering, given its global reach and 4,500 employees.
The account is thought to be worth a six-figure sum, but is understood to be procurement-led and fees are likely to be a key factor in the decision.
DTZ was the subject of takeover speculation earlier this year after its share price lost two-thirds of its value due to tough conditions in commercial property. It retains Blythe Weigh Communications for financial PR.
Meanwhile, Spada has picked up a retained brief with Wates Group, one of the UK's biggest privately owned construction companies.
The agency will support Wates' general corporate profile and highlight its credentials as a sustainable developer and the firm's social commitment.
Earlier this month, Wates Group acquired property repair and maintenance firm Linbrook Services. Spada handled PR around the deal.