The IRS has yet to determine whether or not these values have been inflated. In a 2016 federal filing, SolarCity wrote, "If the Internal Revenue Service or the U.S. Treasury Department were to object to amounts we have claimed as too high of a fair market value on such systems, it could have a material adverse effect on our business, financial condition and prospects." The firm stated, however, that its values were correct and complied with the Treasury Department guidelines. If the Treasury Department or IRS disagrees, SolarCity and other firms could be forced to reimburse institutions that purchase their tax credits as investments. SolarCity received roughly $501.2 million in credits up until December 31, 2015. In SolarCity's 2015 annual report, a note was made stating that if the government determines misrepresentations were made, "the Department of Justice could bring a civil action to recover amounts it believes were improperly paid to us". Since 2006, SolarCity has lowered the minimum FICO score required for customers to get the leasing deals. It uses the score of 650 (a "fair" credit rating) as the cutoff. However, between 2014 and 2017, SolarCity signed long-term lease agreements with at least 14 homeowner customers right before the customers defaulted on their mortgages. The company has been named in 139 lawsuits where it is the defendant in legal proceedings based on "residential foreclosure action". In its response, SolarCity said in a statement to the "New York Times", "Out of more than 305,000 installed customers, SolarCity is currently involved in 139 such proceedings. The litigation is not adversarial – being named in the foreclosure proceeding provides us with advance notice that we need to reassign a contract, and many are immediately resolved with the relevant bank." The Securities and Exchange Commission (SEC) began investigating Sunrun and SolarCity in May 2017, and were looking into whether they adequately disclosed canceled contracts. "Some customers say they canceled contracts after being strong-armed into solar-energy deals" and there have been hundreds of complaints to state attorneys general. The federal government is investigating whether solar companies are "masking how many customers they are losing". The SEC is involved because "investors use that cancellation metric as one way to gauge the companies' health". According to the "Wall Street Journal", "To generate business, solar companies have long relied on thousands of salespeople who knock on doors, make hundreds of cold calls and even trail people as they shop at retailers like Home Depot Inc., according to salespeople, executives and homeowners." SolarCity installed SolarEdge inverter systems with a type of DC-DC converter called an optimizer.