A Conservative AM who is refusing to attend a committee due to an internal party dispute should consider his position, the assembly's presiding officer Dame Rosemary Butler has said.
Byron Davies has failed to show up for eight meetings of the Enterprise and Business Committee in Cardiff Bay.
He will not attend unless new chair, Tory AM William Graham, is sacked.
Mr Davies believes Mr Graham, not previously a member of the committee, was parachuted into the position.
Mr Graham replaced Conservative Nick Ramsey as chair of the committee, when Mr Ramsey was among four AMs sacked from the Conservative front bench team earlier this year.
Mr Ramsay, together with Antoinette Sandbach, Mohammad Ashgar and Janet Finch-Saunders, had rebelled against Welsh Conservative leader Andrew RT Davies in a vote on the devolution of income tax.
On Wednesday, Dame Rosemary made it clear Byron Davies's non-appearance at committee meetings was unacceptable.
"As the national assembly's presiding officer I expect all members, who have been elected to serve on committees, to attend meetings and to take a full part in the committee's business," she said.
"The assembly's committee system plays a central role in scrutinising the Welsh government and developing policy, and should be treated with respect."
She added that AMs unable to attend meetings "should ensure that they arrange a substitute", in line with the rules the assembly operates under.
"If they are unwilling to attend, they should consider their position," Dame Rosemary said.
On Monday, Byron Davies told BBC Wales the decision to remove the four AMs from the shadow cabinet was "ludicrous" and called on his leader to begin "building bridges".
"There are issues within the group, it's not going to go away, it's going to get worse," he warned.
On Tuesday, Andrew RT Davies refused to criticise Byron Davies for not attending the committee, describing the latest party row as political "argy bargy" and saying it was up to Mr Davies what he did.
The Welsh Conservative leader insisted he would not be sacking Mr Graham.