The company reported its board of directors "has determined that it would not be in the best interests of the company to pursue the transaction as presently structured by CDI Corp."

RCM's announcement Thursday came after CDI publicly announced its proposal to acquire all shares of RCM for $5.20 per share in cash in a deal worth approximately $68 million based on 12,999,178 shares.

The proposal was detailed in a letter sent to RCM board members on May 21 and made public on Thursday.

"While we still prefer to work together with RCM and its board of directors to negotiate a mutually beneficial agreement for our respective stakeholders, we feel the significance of this proposal requires us to take our proposal directly to RCM's shareholders," said CDI President and CEO Roger Ballou. "We believe that it is critical to allow the RCM shareholders to evaluate our proposal which would provide significant, certain and immediate value to the shareholders."

CDI's letter said the company held a number of conversations with RCM CEO Leon Kopyt regarding an acquisition, but the talks had not proven fruitful.

CDI, based in Philadelphia, provides engineering and information technology services as well as staffing. Pennsauken NJ-based RCM provides engineering, information technology and commercial staffing.

CDI ranked No. 8 on Staffing Industry Analysts list of largest engineering firms for last year, and ranked No. 27 on the list of largest U.S. staffing firms. RCM ranked No. 19 on last year's list of largest engineering staffing firms and No. 70 on the list of largest U.S. staffing firms.