Sinn Fein does not give its elected representatives "a decisive say" and should reform to become "less of a threat" to democracy, a former Irish justice minister has said.
Writing in the Irish Times, Michael McDowell claimed the party's members had little independence.
Mr McDowell said elected representatives had no real influence on areas such as policy positions, voting intentions, employing officials and party candidacies.
He added that Sinn Fein parliamentarians in Leinster House did not meet as a body to make decisions like other parties.
His comments follow recent polling suggesting a surge in popularity for Sinn Fein as Taoiseach Leo Varadkar seeks a third term in office in Saturday's general election.
Mr McDowell said he could not predict if Sinn Fein would substantially increase its vote, but that it should reform to "become less of a threat to ordinary parliamentary democracy".
He suggested a start would be giving members elected by the public "a real, independent role in our politics".
Sinn Fein should also demonstrate it has turned its back on practices uncovered by the cash-for-ash inquiry - namely "that its ministers deferred completely to unelected party officials on major matters of policy".
Concluding, Mr McDowell added: "Unless Sinn Fein can take these steps, there are eerie echoes of the Weimar republic in the fragmentation and disillusionment so apparent in this week's poll."