By late Tuesday evening, the probability that the budget-balancing, $1.6 billion concession package would be ratified by the state employee unions had reached slim to none.

Union officials confirmed that AFSCME’s P-2 Human and Social Services bargaining unit voted down the agreement, but they refused to release the vote tally until Wednesday morning. There are about 4,200 members in the P-2 bargaining group. They defeated the agreement by 150 votes according to their website.

If the official numbers turn out to be a large margin, the result would make it almost mathematically impossible for SEBAC to approve the tentative deal with so many of AFSCME’s individual members voting against it in various bargaining units . Even though most unions have approved the package, AFSCME, with 15,600 members, is the largest in the coalition and carries the greatest influence in the overall vote.

AFSCME does have one group of Correction Officers that begins voting Wednesday, but the group of 1,850 would have to vote in favor by an overwhelming margin in order to keep alive the possibility of ratification.

In addition to the P-2 bargaining unit, union sources said Connecticut Employees Union Independent Local 511, which represents 4,500 service and maintenance employees, voted down the agreement Tuesday by about 194 votes.

Still, union officials refused to admit defeat with balloting continuing until Friday.

“We remain confident that a strong majority of state workers will support the agreement — despite the concerted efforts of outside anti-public worker parties like the Yankee Institute to disrupt the process,” Larry Dorman, SEBAC spokesman, said in a statement. “Because of the Coalition’s strict voting rules, we don’t know yet if the majority vote will result in ratification of the agreement. Our voting process will continue for the remainder of this week, and the Coalition will have results available by Monday.”

Gov. Dannel P. Malloy was asked early Tuesday about what might happen if the unions fail to ratify the agreement.

“We do have a plan,“ Malloy said. “The exact timing of which, with respect to the legislature, is less important than doing what we have to do almost immediately.”

If the tentative SEBAC agreement fails to receive the votes it needs, then “we have a budget with a gigantic hole that I will begin addressing on day one,” Malloy said.

Malloy has said in the past that without the agreement in place he will be forced to lay off up to 7,500 state employees over the next two years.