This SCP prevents users or roles in any affected account from modifying network connectivity settings including Internet Gateways, NAT Gateways, or VPC Peering.

 
{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Action": [
                "ec2:AttachInternetGateway",
                "ec2:CreateEgressOnlyInternetGateway",
                "ec2:CreateInternetGateway",
                "ec2:CreateNatGateway",
                "ec2:CreateVpcPeeringConnection",
                "ec2:DeleteNatGateway",
                "ec2:DeleteVpcPeeringConnection",
                "ec2:ModifyVpcPeeringConnectionOptions",
                "ec2:RejectVpcPeeringConnection"
            ],
            "Resource": "*",
            "Effect": "Deny"
        }
    ]
}
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