His tweet in support of the women's team came amid allegations of sexual misconduct from former Senate staffer Tara Reade, as well as mounting pressure throughout the week to address them publicly. Biden denied the accusations Friday.
A federal judge on Friday threw out part of an equal pay lawsuit brought by the players that alleged wage discrimination on the part of the U.S. Soccer Federation.
Biden on Saturday urged the team to keep fighting and threatened to withhold funding for the World Cup if the federation doesn't provide equal pay.
"To @USWNT [the U.S. women's national team]: don’t give up this fight," the former vice president wrote. "This is not over yet. To @USSoccer [the U.S. Soccer Federation]: equal pay, now. Or else when I'm president, you can go elsewhere for World Cup funding."
Biden had been under pressure much of this past week to address Reade's allegations on the record, which he did on Friday, denying her accusations from an incident she says took place in 1993.
During a March interview with podcast host Katie Halper, Reade described the alleged incident.
"He greeted me, he remembered my name, and then we were alone. It was the strangest thing," Reade told Halper at the time. "There was no like, exchange really. He just had me up against the wall.”
She continued: “His hands were on me and underneath my clothes, and he went down my skirt and then up inside it and he penetrated me with his fingers and he was kissing me at the same time and he was saying some things to me.”
Biden "unequivocally" denied the allegations on Friday during an interview with MSNBC's Mika Brzezinski on "Morning Joe."
"No, it is not true. I'm saying unequivocally it never, never happened. And it didn't -- it never happened," he said. "I don't remember any type of complaint she may have made. It was 27 years ago and I don't remember -- nor does anyone else that I'm aware of -- and the fact is that I don't remember. I don't remember any complaint ever having been made."
Biden has also recently been pressed about his past statements concerning women coming forward with allegations of sexual harassment and assault.
During the confirmation to appoint now-Supreme Court Justice Brett Kavanaugh, Biden said that “believing women means taking women’s claims seriously." Biden said this week that “women have a right to be heard,” but that their claims should be investigated by the press.
“They should start off with the presumption that they’re telling the truth,” he continued.
“Then you have to look at the circumstances and the facts. And the facts, in this case, do not exist," he added, referring to Reade's allegations.
Biden denied the allegations for a second time on Al Sharpton's MSNBC program "Politics Nation" during a pre-taped interview from Friday evening that aired on Saturday.
"It's not true," he told Sharpton. "I'm saying unequivocally, it never happened. Period."
Fox News' Marisa Schultz and Adam Shaw contributed to this report.