Microsoft has accused patent licensing firm InterDigital of violating US antitrust law by not licensing its standards essential mobile patents on fair terms.
The suit broadens the ongoing battle between the two firms over patent licensing. In April, the US International Trade Commission (ITC) made an initial determiniation in a patent suitInterDigital brought against Microsoft in 2013. The court found some Microsoft handsets infringed two InterDigital wireless patents and its 3G devices could potentially be banned from sale in the US.
Microsoft's antitrust suit, filed on Thursday in a federal court in Wilmington, Delaware, comes as the ITC prepares to make a final decision on the matter this month.
Reuters reported that Microsoft's suit claims InterDigital has engaged in "abusive licensing practices" and falsely promised to license its essential patents on reasonable terms.
Redmond also accused the company of charging exorbitant rates for licensing its patents and argued that InterDigital's "monopolistic conduct" warranted the court ordering InterDigital to stop enforcing its patents.
Additionally, Microsoft said InterDigital was using the threat of the US sales ban to twist Microsoft's arm into settling for a higher price for the patents.
Microsoft inherited its ITC battle with InterDigital after it acquired Nokia's handset business in 2014. The ITC's inital determination in April stemmed from an investigation related to Nokia that dated back to 2007.
The ITC is expected to issue a final determination on August 28.
"InterDigital's research team has a long history of helping drive mobile standards, and our company has always maintained fair, reasonable licensing programs. We will defend ourselves vigorously against Microsoft's suit," InterDigital said.
Microsoft said: "InterDigital falsely promised to license its patents on reasonable terms in order to get them accepted as industry standards, then used that status to charge exorbitant license rates. This violates its commitments, and hurts consumers and competition."
InterDigital has a number of ongoing patents suits against handset makers, including Microsoft. According to InterDigital's latest SEC 10Q filing, 34 percent of its $229m in revenues for the six months to June 30 2015 came from royalties paid by Taiwanese electronics manufacturer Pegatron.