Nastase, 70, a former world number one and two-time Grand Slam title winner, was kicked out of the tie on Saturday after swearing at the umpire, then Britain's pregnant captain Anne Keothavong and their number one player Johanna Konta.
On Friday, he had made a controversial racial slur over Serena Williams's unborn baby while also reportedly propositioning the married Keothavong.
An International Tennis Federation (ITF) statement Sunday read: "The ITF's Internal Adjudication Panel has issued Ilie Nastase with a provisional suspension under the Fed Cup regulations for a breach of the Fed Cup welfare policy at the tie in Constanta.
"Under the terms of the provisional suspension, Nastase may not participate in the Fed Cup in any capacity with immediate effect and shall be denied access to, and accreditation for, any ITF event including Fed Cup.
"The investigation by the Internal Adjudication Panel is ongoing."
Nastase, renowned during his golden era for his pranks, hot-headed unpredictability and being a playboy, ignored the ban on Sunday and turned up at the venue on the Black Sea coast -- he was seen by reporters walking into the VIP lounge.
The ITF later confirmed Nastase was not allowed to be on site in any capacity and the Romanian Tennis Federation president subsequently said he had left.
Nastase's behaviour on Saturday and the day before, when he was overheard making derogatory remarks about US superstar Williams, is being investigated.
After his slur against Williams, who will give birth in September, Nastase was still raging on Saturday.
He was warned twice by the umpire for unsportsmanlike conduct as Konta took on Sorana Cirstea in the day's second rubber.
Nastase screamed at the umpire: "It's not the opera, what's your fucking problem?"
Konta broke down in tears after the abuse -- leading to the rubber being temporarily suspended -- and left the court, subsequently being criticised by her opponent Cirstea for overdoing it.
"With all due respect to Sorana she was not in my shoes on that end of the court being verbally threatened," Konta told the BBC on Sunday.
"Any abuse is not alright, but when it's a couple of metres away from you, screaming at you, I think that's a different ball game.
"It's not something that you truly know how it affects you until you experience it so I do believe she may have been slightly unaware of the events."
Romania had earlier Sunday let their tennis do the talking, sealing the World Group II tie when Irina-Camelia Begu defeated Heather Watson 6-4, 7-5.
However, the victor did not shake hands with her opponent at the end of the rubber, according to reporters courtside.
Simona Halep -- who on Saturday had urged the crowd to calm down -- had earlier put the hosts in control by beating Konta 6-1, 6-3.
Defeat relegated Britain to the Europe/Africa Zone.
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