A UKIP AM discussed with an assembly official how an advert for a job in her office could be changed to help her brother get an interview for the post.
Michelle Brown was told that if she used an initial draft of the advert her brother would be “sifted out”.
She was also asked if she wanted to “check” with him what qualifications he had before finalising the advert.
North Wales AM Ms Brown said she had acted with “complete propriety”.
The institution refused to release under the Freedom of Information Act full details of an exchange between Ms Brown and an assembly official where they discuss what qualifications her brother has.
But BBC Wales understands that following an initial discussion about his qualifications the official wrote to Ms Brown: “If we go ahead with the qualification that’s in the job description [an NVQ] Richard [Ms Brown’s brother] will be sifted out before the interview stage.
“Do you want me to change it to [GCSE] Grade C or above in English?”
Ms Brown replied: “Can it [the NVQ] be downgraded to desirable?”
The official then said: “We do need to have some qualification in the essential [section of the advertisement], do you want to check with Richard what he has?”
Ms Brown replied: “Fair enough! Shall we just leave it as GCSE English and Maths at Grade C or equivalent?”
The official then told her “that’s fine”.
The job advert was for a receptionist and personal assistant, to be paid between £18,536 and £24,593 a year.
The NVQ requirement was not included in the final advertisement.
BBC Wales understands Ms Brown’s brother did not get the job.
The assembly said its recruitment panel recommended someone else to Ms Brown and she will meet that person next week to discuss the position.
But her brother is still listed on the register of members interests as a constituency caseworker for the assembly member and he has been in that role since June 2016.
AMs are allowed to appoint staff on a temporary basis for a six month period after being elected without having to put in place a formal recruitment procedure.
BBC Wales understands concerns have been raised within UKIP about Ms Brown’s brother’s performance.
A total of 12 AMs have declared on the register of interests that they employ relatives.
In 2009, an independent report recommended the appointment of family members be stopped.
Defending her handling of the recruitment process for her office, Ms Brown said: “I appointed Richard upon my election to the assembly, as I needed someone to deal immediately with constituency issues.
“Confidentiality and personal loyalty are essential elements in the job description of all AMs’ staff.
“When his temporary contract expired, he was not re-appointed.
“The Assembly Commission is intimately involved in devising job descriptions for open competition and, in the case of AMs’ family members, they interview candidates independently of the AM.
“I have acted at all material times on the advice of the commission and with complete propriety.
“Any suggestion to the contrary from within UKIP should be discounted as sour grapes from someone with an axe to grind.”
Asked about the matter on BBC Radio Wales, UKIP assembly group leader Neil Hamilton said: “The assembly commission is entirely responsible for job descriptions.
“All these jobs have to be publicly advertised and in the case of somebody who is a family member who is an applicant then the appointment decision is taken by the assembly itself, not by the individual AM.”
In November 2016, Mr Hamilton defended the employment of his wife Christine as his personal assistant on the same grounds.
In a statement, the National Assembly for Wales Commission, which overseas appointments at the body said: “The principles of fair and open competition based on merit apply to all posts advertised for assembly member support staff.
“The appointment of the employing assembly member’s family members is only permissible where the member plays no part in the assessment and interviews, which are instead conducted by the members’ business support team.”
Asked about the email exchange involving Ms Brown, an assembly spokeswoman said: “It is entirely appropriate, and within the rules, for Members’ Business Support to work with individual Assembly Members to establish selection criteria and arrangements for a particular appointment.”