To plastics manufacturers Toray and Polytop said the rise in electricity costs coming from the project and its PPA would damage their businesses
The attorney representing the two companies said the PPA does not meet the law authorising the wind farm, which requires it to be "commercially reasonable". It also claimed only six permanent jobs would be created from the project.
A decision is expected by the end of the year.
The Block Island PPA was agreed last year for 24.4 cents per KW/h. However, the deal sets the price as an upper limit for the first year and leaves the possibility the price will be reduced the initial period.
There have been a number of challenges to the National Grid PPA.
In February, new Rhode Island attorney general Peter Kilmartin dropped a lawsuit challenging Deepwater Wind’s plans to build the 28.8MW Block Island offshore project.
The case centred on the former Rhode Island attorney general Patrick Lynch’s decision in August to request the Supreme Court abolish the project's power purchase agreement with National Grid.
Deepwater Wind eventually hopes to build a 1GW project off Rhode Island. The Block Island wind farm is a precursor to provide a business case for the larger development.