Surapong Tovichakchaikul, a former deputy prime minister and foreign affairs minister, said after discussions, Pheu Thai was unlikely to send anyone to compete for the NRC seats for three reasons.
First, the party is not certain its candidates will be selected by the National Council for Peace and Order (NCPO).
Second, the quota allowed — two for each organisation — is too small.
Third, Pheu Thai is viewed as a party to the conflict so it is not appropriate.
The complicated process of selecting NRC candidates has begun, with 88 selection committees set to propose up to 935 candidates to be shortlisted by the NCPO to 250.
Mr Surapong also said the party had made no move since the coup.
"We're waiting for the processes to draft a new constitution to finish and also for the election, for which we are always ready."
After hearing NCPO chief Prayuth Chan-ocha speak on Friday, Mr Surapong said he supported what the general was doing.
"I support any move to tackle corruption. I also thank him for launching the rice stock audit, which found a small amount missing. In any case, responsible persons must be held accountable," he said.
Asked about the National Legislative Assembly (NLA), Mr Surapong said he would rather not comment.
"I only hope the NLA will not act like the Group of 40 Senators and that it will pass laws that are fair to all sides."
At parliament on Saturday, 38 NLA members reported for duty in the morning.
They include Pialipan Sombatsiri, CEO of Nai Lert Park Hotel Co Ltd; Sakthip Krairiksh, former foreign affairs permanent secretary; Gen Ood Buangbon, a former NLA member in 2007 and former close aide to Privy Council president Gen Prem Tinsulanonda; Adm Kamthorn Poomhirun, an former navy commander; Adm Amornthep Na Bangchang, deputy supreme commander; and Lt Gen Thirachai Nakvanich, Army Region 2 commander.