Royal Mail broke law with their bid to change charges
Royal Mail broke competition law when it tried to change the way it charged rivals such as Whistl for use of its network, according to provisional findings by regulator Ofcom.
Whistl complained to Ofcom after the changes were announced in January last year, prompting an investigation.
Royal Mail suspended the move in March 2014 and said in March this year it had withdrawn the changes.
Ofcom said its provisional view was that Royal Mail "breached competition law by engaging in conduct that amounted to unlawful discrimination against postal operators competing with Royal Mail in delivery".
The group will now be able to make representations to the regulator before it takes a final decision. It said it was disappointed by the announcement and considered the changes it had planned were "fully compliant with competition law".
Ofcom has the power to fine Royal Mail up to 10% of its annual turnover. Revenues for the year to the end of March totalled £9.3 bn.
Dutch-owned Whistl, formerly known as TNT, suspended deliveries in May after private equity backer LDC pulled out of funding to help expand the business.