Gareth Clubb called for Neil McEvoy's Adjudication Panel for Wales hearing on 2 and 3 March to be delayed.
Plaid's spring conference is being held in Newport on 3 and 4 March.
The Adjudication Panel for Wales has been asked to comment.
Mr Clubb said the clash "could lead to an erosion in public trust" in the work of the panel.
Mr McEvoy, a Plaid AM for South Wales Central and the party's group leader on Cardiff council, is facing a tribunal over allegations he brought the authority into disrepute in his role as a local councillor.
BBC Wales reported in January that the case, referred to the tribunal by the Ombudsman, apparently relates to whether a comment was made to a council officer in a threatening way.
In a letter to the panel, Mr Clubb said the Fairwater councillor "will be speaking at the conference and we would not wish his speech to be disturbed either by his appearance at a panel or by his having to prepare for an imminent hearing".
He said the case "could have been heard at almost any point in November through February on a date that would not have conflicted with a critical date in the political calendar".
Mr Clubb, who has served as Plaid's chief executive since last September, said timetabling the hearing for the day of the conference gave the "appearance of political interference, even if the date clash is entirely coincidental.
"I fear that scheduling Mr McEvoy's case to coincide with our spring conference fails this test and could lead to an erosion in public trust in the work of the panel."
In the letter Mr Clubb suggests it could be seen "that the panel is trying to unfairly prevent [Mr McEvoy's] appearance at conference".
He said an "impartial decision" would rightly determine that the "proposed date is manifestly unfair to Mr McEvoy".
Mr Clubb, who said the dates of the conference had been public knowledge since November, called for the hearing date to be changed so it avoided the conference and the "formal local election period".
Council elections take place on 4 May.
The scheduling of a tribunal into the behaviour of a Plaid Cymru AM at the same time as his party's conference gives the appearance of political interference, the party's chief executive has said.