The review, which also includes its corporate communications, covers the German electronics company's entire B2B comms business, including above the line, direct, media, digital and PR.
Agencies have already received requests for information, and chemistry meetings are set to take place next week. It is thought that a shortlist of three agencies from each channel will be pulled together and that pitches will begin in early May.
The review is being run out of the company's German head office.
The winning agencies will be briefed to work closely together to create a new B2B strategy for the company, with much of the lead creative coming out of the appointed digital agency.
A spokeswoman for Siemens said: "Last April, Siemens launched a new supply chain management initiative to improve the efficiency of its co-operation with suppliers but we do not comment in detail on single suppliers."
Earlier in the week, it was reported that the electronics giant was cutting 4,200 staff, more than 10 per cent of its global workforce, from its IT unit. The cuts include 2,000 in Germany and will be implemented by autumn 2011.
This announcement came despite the company's recent financial results showing a rise in net income. For the last three months of 2009, it posted income of £1.36 billion, a 24 per cent growth compared with the same period last year.