The subpoenas are part of an investigation started by Crist's office in February after the vendors' alleged snub of the county indirectly caused it to be in violation of Florida and federal election laws.
The subpoenas issued to Election Systems & Software Inc. (ES&S), Diebold Election Systems Inc. and Sequoia Voting Systems Inc. are seeking copies of documents related to their sales of e-voting machines in Florida since 2003.
Crist said the probe was launched to determine whether the companies, which have done business throughout Florida over the past three years, privately agreed to withhold their gear from Leon County and its elections supervisor, Ion Sancho.
"These subpoenas are to ensure that the rights of our voters with disabilities, as well as all Florida voters, are secured," Crist said in a statement.
The relationship between Sancho and voting machine vendor Diebold has been rocky in recent months as the elections supervisor has become an outspoken critic of touch-screen voting systems.
In December, the Leon County Commission -- at Sancho's urging -- voted to replace its Diebold AccuVote optical-scan gear. Sancho cited concerns about the security of the systems and their inability to adhere to federal Help America Vote Act requirements and state election laws.
Days after the vote to replace the Diebold machines, Sancho reached an informal agreement to buy $1.8 million worth of voting equipment from ES&S. That deal fell through a month later, leaving the county facing an order from the Florida secretary of state's office to repay a US$500,000 grant that had been earmarked for the machines.
Sancho suggested that the vendors refused to sell their machines to Leon County "because they could. The laws of Florida offer no protection to elections officials."
The vendors had varying responses to the attorney general's action.
Diebold declined to comment on the subpoenas, but a spokesman contended that the company did not refuse to sell equipment to Leon County; rather, the relationship was terminated by Sancho.
ES&S also said it is reviewing the questions and document requests. A spokesman said only that "after evaluating all of the information available to us, we reluctantly determined that we could not expect to have an effective partnership with [Leon County]."
Sequoia said that the complaint is without merit and promised to fully cooperate with any government investigation.