Nearly 1,600 childcare and early years providers are set to reject proposals for better pay and conditions for employees because they are not being allowed to take part in negotiations.
The Programme for Government contains a commitment to examine the introduction of a legally binding Joint Labour Committee to underpin remuneration and conditions for workers in the sector.
It is a bid to address low pay, which is believed to hamper recruitment.
However, small business body ISME said the JLC will be "unacceptable" if the body representing the majority of employers in the sector is excluded from negotiations.
In correspondence with Taoiseach Micheál Martin, Tánaiste Leo Varadkar and Minister for Children Roderic O'Gorman, ISME Chairman Ross McCarthy stated: "It is untenable for you to proceed with a JLC where the representatives of a substantial majority of providers are excluded.
"It will fatally undermine the credibility of any agreements reached, and you can have no legitimate expectation of support, buy-in or acceptance from our members if this exclusion persists."
ISME pointed out that its affiliate - the Federation of Childhood Providers - has 1,585 members, while what it called the "entity" (Childhood Services Ireland/ibec) purporting to represent the entire sector has around 580 members.
"These figures of course exclude significantly larger numbers of stand-alone 'sole trader' Early Years providers operating outside the larger towns and villages," the ISME chairman noted.
He said that if ISME is not included in negotiations, the proposed JLC should be abandoned.
Mr McCarthy also strongly criticised ISME's exclusion from the Labour Employer Economic Forum (LEEF).
The Department of Children, Equality Disability, Integration and Youth stressed that the process of examining whether establishing a JLC would be suitable was not undertaken under the LEEF.
It noted a pre-JLC investigation overseen by former Labour Court Chair Kevin Duffy: "The report concludes that all parties agreed that the establishment of a JLC is the most appropriate means by which pay and conditions of employment in the sector can be addressed.
"Under the Industrial Relations Act 1946, the question of which representative bodies should participate in a JLC is a matter for the Labour Court, if an Establishment Order is agreed to.
"No determination has yet been made as to which bodies would participate in a JLC for the ELC and SAC sector..."
The Department of Enterprise, Trade and Employment confirmed that Minister Leo Varadkar is considering a request to submit an application to the Labour Court for the establishment of a JLC.
Meanwhile, ibec defended its role in the JLC process involving SIPTU and CSI/ibec established at the direction of Minister O'Gorman under the Programme for Government.
It said the pre-JLC process chaired by Kevin Duffy had determined there was "substantial agreement between the representative parties to the establishment of a Joint Labour Committee".
The spokesperson said it now falls to the Labour Court to prepare a draft establishment order, and to carry out an inquiry.
"With regard to representation of interests in the establishment of a Joint Labour Committee, as set out above, that is a matter for the Labour Court under the Industrial Relations Act, 1946," the spokesperson concluded.
