Am I allowed to write to the EPO about a patent application filed by another company concerning a product developed by our company?

Yes. Under Article 115 EPC, any third party may file observations concerning the patentability of an invention claimed in a published European patent application. They must be filed in writing in an EPO official language (English, French or German), and must state the grounds on which they are based. There is no prescribed EPO form for this. The person submitting the observations is not a party to the patent grant proceedings, and is therefore not informed by the EPO about their further outcome.

The observations are communicated without delay to the applicant or proprietor, who may comment on them. If they call into question the patentability of the invention in whole or in part, they must be taken into account in any proceedings pending before a department of the EPO until such proceedings have been terminated, i.e. they must be admitted into the proceedings. If the observations relate to alleged prior art available other than from a document, e.g. from use, this should be taken into account only if the alleged facts either are not disputed by the applicant or proprietor or are established beyond reasonable doubt. Observations by third parties received after the conclusion of proceedings will not be taken into account and will simply be added to the file (see Guidelines for Examination, E-VI, point 3 and Rule 114 EPC).