(CNN) -- The New Jersey Supreme Court on Friday denied the state's request to temporarily prevent same-sex marriages, clearing the way for same-sex couples to marry in the state starting Monday.
Gov. Chris Christie's administration appealed -- and asked the court to delay -- a lower court's September 27 order that the state must allow same-sex couples to marry beginning October 21, rather than give them the label "civil union."
The appeal will be heard in January. But the state Supreme Court on Friday declined to delay the September order in the meantime, writing that "the state has not shown a reasonable probability that it will succeed on the merits" of the appeal.
"When a party presents a clear case of ongoing unequal treatment, and asks the court to vindicate constitutionally protected rights, a court may not sidestep its obligation to rule for an indefinite amount of time," the 20-page decision read. "Under those circumstances, courts do not have the option to defer."
Among the arguments it rebutted, the high court said the state failed to explain how it will "suffer irreparable harm in a number of ways" as a result of the lower court ruling.
"The State has presented no explanation for how it is tangibly or actually harmed by allowing same-sex couples to marry. It has not made a forceful showing of irreparable harm," the decision read.
In an e-mailed statement to CNN, Christie's spokesman Michael Drewniak said, "The Supreme Court has made its determination. While the Governor firmly believes that this determination should be made by all the people of the State of New Jersey, he has instructed the Department of Health to cooperate with all municipalities in effectuating the order of the Superior Court under the applicable law."
The state attorney's general's office didn't immediately return a phone call seeking comment as of Friday afternoon.
Some ceremonies already are planned for Monday. U.S. Sen.-elect Cory Booker, the current Newark mayor, plans to recognize the marriages of several same-sex couples at 12:01 a.m.
Marriage-rights groups on both sides reacted strongly.
"It is extremely disappointing that the New Jersey Supreme Court has allowed the ruling of an activist judge to stand pending its appeal through the court system," said Brian Brown, president of the National Organization for Marriage, which opposes same-sex marriage. "All in all, today's ruling is another sad chapter in watching our courts usurp the rights of voters to determine issues like this for themselves."
But Troy Stevenson, executive director of gay-rights group Garden State Equality, said the high court's decision means "the door is open for love, commitment and equality under the law."
"This is a huge victory for New Jersey's same-sex couples and their families." added Hayley Gorenberg, deputy legal director of gay rights group Lambda Legal and the organization's lead attorney on the case. "Take out the champagne glasses -- wedding bells will soon be ringing in New Jersey!"
In the September ruling, Judge Mary Jacobson of Mercer County Superior Court argued that civil unions, which the state already allows same-sex couples, don't go far enough because they, in some cases, illegally prevent them from getting federal benefits.
Her ruling cited the U.S. Supreme Court's June rejection of part of the federal Defense of Marriage Act, a move that ensured same-sex spouses legally married in a state may receive federal benefits.
After the DOMA ruling, some federal agencies are extending benefits to legally married same-sex couples, but denying them to same-sex couples in "civil unions," Jacobson wrote.
"If the trend of federal agencies deeming civil union partners ineligible for benefits continues, plaintiffs will suffer even more, while their opposite-sex New Jersey counterparts continue to receive federal marital benefits for no reason other than the label placed upon their relationship by the state," Jacobson wrote.
"This unequal treatment requires that New Jersey extend civil marriage to same-sex couples to satisfy the equal protection guarantees of the New Jersey Constitution," she continued.
Jacobson ruled on a lawsuit filed aggainst the state by six same-sex couples and their children, as well as Garden State Equality.
Her ruling came more than a year after Christie vetoed a bill that would have legalized same-sex marriage in the state.
New Jersey has recognized civil unions between same-sex couples since 2007, after the New Jersey Supreme Court ruled that the state must allow same-sex couples all the rights and benefits of marriage. As far as state rights and benefits went, civil unions and marriages differed only in label, Jacobson noted.
New Jersey is one of four states that offer civil unions, but not marriage, to same-sex couples. The others are Colorado, Hawaii and Illinois.
Same-sex marriage is legal in 13 U.S states -- California, Connecticut, Delaware, Iowa, Maine, Maryland, Massachusetts, Minnesota, New Hampshire, New York, Rhode Island, Vermont and Washington -- as well as the District of Columbia.
Same-sex marriage is banned in every state not mentioned above, except for New Mexico, which has no laws banning or allowing it.
CNN's Bill Mears, Bryan Koenig, Rob Frehse and Kevin Conlon contributed to this report.