Government Procurement Law
Section 55. Modification and Withdrawal of Bids. - Bidders may modify their bids: Provided, That this is done before the deadline for the receipt of bids. The modification shall be submitted in a sealed envelope duly identified as a modification of the original bod and stamped received by the BAC.
Bidders may, through a letter, withdraw their bids or express their intention not to participate in the bidding before the deadline for the receipt of bids. In such cases, they shall no longer be allowed to submit another bid for the same contract either directly or indirectly.