TNT Post UK has submitted a formal complaint to regulator Ofcom claiming that rival Royal Mail has breached its regulatory conditions.

TNT’s complaint comes after Royal Mail revealed it would be changing the terms of the contracts it holds with other mail carriers, including the price it charges for final mile delivery.

A spokesman for TNT Post was unable to disclose the details of the complaint.

“TNT Post has submitted a formal complaint to Ofcom based upon a breach of Royal Mail’s regulatory conditions,” he said.

“The complaint has been accepted and is currently being investigated by Ofcom. The investigation is expected to be concluded in the second half of 2014.”

In a statement, Royal Mail said TNT Post’s complaint was “unfounded”.

“We considered carefully our legal and regulatory obligations before notifying Access customers of the changes,” the statement said.

TNT Post is currently rolling out a final mile delivery service of its own across the UK to challenge Royal Mail’s. Parent PostNL entered into a joint venture with private equity firm LDC last year to provide funding for the project.

Changes to Royal Mail’s contracts are due to come into effect on 31 March and will affect 31 customers.