ITV claims that STV owes it money because in opting out of showing certain programmes it is "not honouring its contractual contributions towards the network budget".
Today STV has filed its own claim, centring on new media rights, in addition to submitting its defence to ITV's claim.
STV is seeking up to £12m in damages claiming that ITV is exploiting new media rights without its consent.
In its defence against ITV, it has submitted a claim against the company for £35m and an additional counter-claim "in respect of the conduct of the airtime sales agreement by ITV Consumer".
STV said it is also expecting to file further claims regarding "significant prejudicial behaviour on the part of ITV Network and ITV plc".
In reaction, ITV accused STV of making "no more than a diversionary tactic to distract from the significant sums which STV owes to ITV".
An ITV spokesman said: "ITV Network has always entered into agreements for the benefit of all Channel 3 licensees and strongly disputes any allegation by STV to the contrary.
"It is also important to note that STV is already being paid a revenue share on deals which have been struck on behalf of all licensees and therefore any claim that STV has suffered financial loss is baseless."