National's Judith Collins says party leadership rival Amy Adams broke a rule by bringing an entourage of supporting members to the launch of her campaign.
"The fact is that the caucus agreed that we would not all come out and be counted and those sorts of things until after the vote. I'm sticking by the rules," Ms Collins said.
However, party whip Jamie Lee-Ross backed Amy Adams saying there was not agreement on taking public positions.
Other main leadership rival, Simon Bridges, was also uncritical of Ms Adams public show of support.
"I think Amy is absolutely entitled to do what she did," Mr Bridges said.
"My person view in relation to supporters that I have is I'm not encouraging them to go out."
Meanwhile, veteran Jonathan Coleman has ruled himself out of the race for party's the top spot.
Selwyn MP Ms Adams announced she would be running to replace Bill English - who on Tuesday revealed he would be resigning this month - flanked by four fellow MPs who proceeded to publicly endorse her.
Ms Collins today told reporters the party's caucus had agree to not make public displays of support.
However, Chris Bishop, one of Ms Adams' accompanying quartet, seemed to view the situation differently.
"I haven't seen Judith's comments, but there's nothing to stop people endorsing leadership candidates," he said.
"It happened in the transition from John Key to Bill English ... there may be others who come out over the next few days or next week who endorse candidates. We just have to wait and see. Just for me, I've made up my mind."
Relative dark-horse Mark Mitchell and National Party veteran Steven Joyce are both still considering possible runners - but neither was in Wellington today.
However, former health minister Dr Coleman has now ruled himself out.
He declined to say who he'd back.
"I think we've got three great candidates and I've made my decision on the basis of who is going to be best to beat Labour in 2020. I think that person is among those three," he told reporters.
The third confirmed current contender in the race is Tauranga MP Simon Bridges.
While Ms Adams has the backing of members Nikki Kaye, Mr Bishop, Maggie Barry and Tim Macindoe, others were staying tight-lipped today.
"I'm taking my time," said Todd McClay.
"I'm going to take some soundings but I'm not going to do that through the media."
Brett Hudson had a similar attitude.
"There's some way to go before we make a final decision," he said.
Mr English's resignation takes effect on February 27 and the 56-member caucus has to elect a new leader before then.
There will be a secret ballot, with low-polling contenders dropping out until one has a clear majority.