BDO USA, the Chicago-based business accounting and advisory firm with $1.5 billion in yearly sales, says it is adding up to 100 professionals from Philadelphia-based management-consulting firm AC Lordi, as of June 1.

Frank Lordi, the Philadelphia firm’s founder, has joined BDO as an advisory partner, he said in a statement. Six other Lordi principals also become partners at BDO, which already has a Philadelphia office, which works with life-sciences, manufacturing and financial companies.

“We are stronger together than apart,” Frank Lordi said in a statement.

Lordi is the latest in a series of Philadelphia financial consulting or accounting firms to join larger national companies in recent years. Lordi, a Penn State grad, is a former Arthur Andersen manager. His corporate clients have included Crown Holdings, Trinseo, Unisys, and other large Philadelphia-based employers.

By size, BDO ranks with Grant Thornton in the second tier of U.S. corporate accounting and related services companies, below the so-called “Big Four" — PricewaterhouseCoopers, Deloitte, Ernst & Young, and KPMG, which service the largest corporations.

“Each of the Big Four firms has significant advisory and consulting practices,” and frequently look for smaller firms with corporate advisory clients they can add, said John McLaughlin, founder of AuditExchange, based in Newtown Square, and a former parter at BDO and at Smart & Co., now part of Grant Thornton.

“For a lot of big firms, the consulting business has become larger” than traditional tax and accounting, he added. That makes a firm like Lordi, with its midmarket corporate clients, especially valuable to an outfit like BDO. (Story has been updated to make clear that Lordi is primarily a consulting firm.)