The members have been told they would only be able to employ one adviser as part of their staffing allocation in the new parliamentary term.
Under the previous coalition government, crossbench MPs and senators were allowed to have two advisers and two assistant advisers.
The prime minister wrote to crossbench MPs and senators on Friday advising them of the changes.
"I propose to allocate you one additional full-time staff member at the adviser classification, in addition to your four electorate staff," the letter said.
"My government intends to increase resourcing to the parliamentary library to reflect the support role that it plays to parliamentarians, particularly those on the crossbench."
The prime minister also told crossbenchers parliament department officers would be made available for advice on procedure as well as help in drafting private member's bills.
In a joint statement, crossbench senators Jacqui Lambie, Tammy Tyrrell, David Pocock, Pauline Hanson and Malcolm Roberts said the decision was an attack on democracy.
"This act, at the beginning of this new parliament and new government, has significantly damaged relationships with the crossbench," the statement said.
"It flies in the face of earlier remarks from the prime minister that he was hoping for a more collaborative term of parliament, where members and senators from across party lines could come together to genuinely improve conditions for Australians."
In a separate statement independent MP Monique Ryan, the member for Kooyong, said previous staffing levels recognised the workload of independent MPs was significantly greater than that of party backbenchers.
"This measure is an attack on the crossbench, on its ability to function effectively and independently, to improve legislation, and to hold the government to account," she said.
A Labor spokeswoman said staffing numbers were reviewed and reallocated after every election.
The new parliament, which sits from late July, will have 12 independent or minor party MPs in the House of Representatives, while there will be six in the Senate.
The joint statement from the five crossbench senators urged for the prime minister to reconsider the decision.
"This cut will only further deteriorate conditions in parliament, and make it impossible for crossbench senators to carefully interrogate legislation, hold the government to account and ensure we are supporting laws that are in the best interests of our communities and our nation," the statement said.
"We reject comments that senators could draw on electorate staff to help with parliamentary duties. This takes away from the ability of senators to properly represent their communities and engage with people on issues in parliament."
