BEA Systems Inc said on Friday it still cannot accept the $17-per-share takeover bid from Oracle Corp as it significantly undervalues the business software maker.

As fiduciaries, our board cannot endorse a proposal that it has concluded significantly undervalues BEA. We therefore assume that your proposal will expire on October 28, BEA's vice president of business planning and development, William Klein, said in a letter to Oracle President Charles Phillips.

Oracle has said its $6.7 billion bid for BEA will expire at 5 p.m. California time on Sunday.

(Reporting by Tiffany Wu, editing by Gerald E. McCormick)