Smith-Gander said Ferrovial's offer lodged on 7 December was for a cash consideration of $1.35 per share, which she said compares poorly with the trading prices of the firm over the last 12 months.
She added that the performance of the company (formerly Transfield Services) has continued to improve in the last 12 months, the outlook is positive, and the diversified portfolio approach is successful.
The Broadspectrum board has recommended that shareholders "do nothing" until they have received the detailed response in January 2016.
Ferrovial posted an updated bidder's statement on the Australian Stock Exchange, but the offer has not been amended.
UBS and Allens is advising the Spanish construction giant on the deal, which would be funded with existing cash reserves and bank facilities.