(Providence, RI) -- Four people are pleading guilty to tax charges connected to an investigation into payments of vendors who performed maintenance on U.S. Postal Service vehicles in Rhode Island. The U.S. Justice Department says the cases began as a fraud investigation related to companies controlled by Ronald and Cheryl Long of Warwick, who provided the mechanical work. The Longs allegedly put false information on their tax returns and did not file a return in 2011. Retired Warwick postmaster Gary Neirinckx, who opened a business in Warwick co-owned by the Longs, admitted to accepting payment from the Longs in exchange for recommending mechanical services to other postmasters, but prosecutors say he didn't report the income on his tax returns.