Premier Rugby has warned the Rugby Football Union it intends to take legal action over payments for Lions players. An RFU statement read: "The RFU has been advised legal proceedings will be initiated within seven days, unless certain undertakings are received."
Premier Rugby is acting for three clubs who have been denied �120,000 in total for providing players for Lions duty.
But the RFU says the �15,000 per player deal was conditional on each being rested for 11 weeks after the tour.
The RFU, which has now referred the matter to its lawyers, said that eight players on Lions duty played for more than 40 minutes in matches inside the timeframe.
The players involved are Sale quartet Jason Robinson, Mark Cueto, Charlie Hodgson and Andrew Sheridan, Leicester duo Martin Corry and Julian White, and Wasps pair Matt Dawson and Simon Shaw.
As a result, Sale have had �60,000 held back while Leicester and Wasps will not get �30,000 apiece.
However, Premier Rugby has stated that it "does not accept that an authorised agreement was reached on the rest periods for English Lions."
It added: "We are extremely disappointed that the RFU has adopted this position. We are now reluctantly considering the actions open to us on behalf of clubs to recover the unpaid monies with interest."