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.