Santiago says the accord circumvents a constitutional ban on foreign military bases because of the continued presence of US troops in the country over the past 10 years.
However, the Philippine government defended its agreement with the US on visiting forces as "important, useful and relevant".
"The Department of Foreign Affairs respects the views of the senate and will consider the comments and concerns they have expressed on the Philippines-United States Visiting Forces Agreement," the DFA said in a statement.
In defence of the treaty, the DFA stressed that the VFA, which was signed in 1998, is indispensable to the nation's security.
"The Philippines' relationship with the United States in general, and its defence and security co-operation in particular, constitute a strategic partnership that is long-standing and mutually beneficial. With no other country does the Philippines have such deep and diversified ties," the statement said.
The VFA governs the treatment of US servicemen in military units and defence personnel who are on Philippine territory for short periods for joint military exercises approved by both the Philippine and US governments.
It entered into force in May 1999, eight years after the closure of US military bases in the Philippines in 1991.