The Speaker of Parliament has no powers to decide if a motion of no confidence vote should be conducted through a secret ballot or not, Speaker Baleka Mbete has said.

Mbete was responding to a letter from the United Democratic Movement's (UDM) lawyers demanding a secret ballot for the motion of no confidence vote against President Jacob Zuma.

The motion will be debated in Parliament on Tuesday, April 18, following Zuma's Cabinet reshuffle last week which saw five ministers lose their jobs.

"Our client has reason to believe that the outcome of the vote might be unduly tainted by allegiance to extraneous considerations other than 'faithfulness to the republic and obedience to the Constitution'.

"In particular, our client is in possession of evidence of intimidatory tactics aimed at the voters by senior members of the ruling ANC [African National Congress], including statements that those who may vote in favour of the motion will be expelled from Parliament. This will defeat the purpose of even holding the vote," the UDM said through its lawyers on Thursday.

It was in the interest of the public for the proposal to be accepted, the party said.

Parliamentary rules also do not prohibit the use of a secret ballot in a motion of no confidence vote, the UDM added.

"Voting procedures in the assembly are determined by the Constitution and the rules of the assembly," Mbete said in response on Friday.

"Your client's demands that the motion of no confidence be determined by way of secret ballot cannot be acceded to, as it does not have any basis in law," Mbete told the UDM.