The Supreme Court said Friday it will hear arguments in a legal fight between Salt River Project and Tesla Motors.

In a class-action lawsuit, Tesla (owner of SolarCity) said Salt River Project (SRP) is acting in a monopolistic manner by imposing unfair fees on potential solar power purchasers. Salt River responded that it can’t be sued in a class action – and that issue is what is headed to the Supreme Court.

In the original 2015 case, attorneys for Tesla said SRP’s new pricing plan approved amounts to a penalty on customers when demands exceed what solar systems can produce.

That penalty, according to Tesla lawyers, is about 65 percent over prior rate plans. That compares with an average 3.9 percent increase for residential customers who buy all their power from SRP.