The decision by the Senate's parliamentarian, Elizabeth MacDonough on Saturday, deals a blow to Trump and his administration, which has sought the money for security purposes related to the ballroom.
Trump has said construction of the ballroom will be funded by private donors. But Senate Republicans are seeking $US1 billion ($A1.4 billion) in taxpayer funding to the Secret Service for security upgrades, including the ballroom.
The parliamentarian interprets Senate rules including whether legislative provisions are permitted.
Trump's fellow Republicans control the Senate, and they still could revise the legislation to try to gain the parliamentarian's approval.
If they do not succeed, they may be unable to include the ballroom-related funding in a $US72 billion ($A101 billion) spending package they plan to bring to a vote on the Senate floor, with passage expected on a party-line vote with Democrats opposed. The bulk of the legislation is devoted to immigration enforcement.
Republicans are invoking complex budget rules to try to be able to secure passage without any Democratic support. Democrats have opposed funding for Trump's signature immigration crackdown absent reforms they have sought since federal immigration agents killed US citizens in separate incidents in Minnesota in January.
Republicans hold a 53-47 majority in the Senate, leaving them short of the 60 votes needed to pass most legislation under the chamber's rules.
Democrats have criticised the ballroom as an expensive and frivolous diversion by Trump at a time when Americans face rising costs such as higher fuel prices. Trump, a real estate developer turned politician, has written on social media that it will be "the finest Building of its kind anywhere in the World."
Republicans have said the ballroom-related spending they are pursuing is needed to ensure presidential safety, citing an April incident in which a gunman tried to storm a black-tie media gala in Washington that Trump attended.
The administration has said the ballroom will modernise infrastructure, bolster security and ease strain on the White House, which often relies on temporary outdoor structures to host large events.
Trump has said the ballroom will be completed around September 2028, near the end of his second term in office.
Democrats, hoping to win control of Congress in November's midterm elections, are seizing on Republican support of the ballroom to portray Trump's party as out of touch with the cost-of-living concerns of Americans at a time of rising energy costs driven by the Iran war he launched in February.
