WASHINGTON (AP) — An Internal Revenue Service official refused to testify Wednesday before a House committee examining his relationship with the CEO of computer services company that has as much as $500 million in contracts with the tax agency.

Gregory Roseman said he was advised by his lawyer to invoke his constitutional right against self-incrimination. The House Oversight and Government Reform Committee is investigating government contracts secured by Strong Castle Inc., and whether a friendship between Roseman and Strong Castle’s CEO, Braulio Castillo, was a factor in the company’s ability to win such large contracts with the IRS.