Labour Party Leader Ed Milliband will make sweeping changes to the way his party and its affiliated trade unions interact in what is being heralded as the biggest party reforms in a generation, Sky News reports Tuesday.

The changes come after the party faced allegations of attempting to sign up hundreds of members to Labour to fix candidate selection in Falkirk, Scotland. The scandal is now the subject of a formal police investigation.

In previous years, the 15 trade unions associated with the Labour Party would enroll up to 3 million members a year as Labour Party members. This would give the party a huge membership and about $12.3 million annually.

Milliband's reforms could threaten the party’s relationship with trade unions, most notably Unite, the country's largest union, and its leader, Len McCluskey. Unite's power over Labour is expected to decline after the reforms are implemented.

The new plans will allow union members to opt in or out of Labour Party membership rather than being signed up automatically. This will initially leave the party short of funds and members, but according to party insiders, it will strengthen the party's relationship with unions in the long term.

“I do not want any individual to be paying money to the Labour Party in affiliation fees unless they have deliberately chosen to do so," Milliband said. “I believe we need people to be able to make a more active, individual choice on whether they affiliate to the Labour Party. This idea has huge potential for our party and our politics. It could grow our membership from 200,000 to a far higher number, genuinely rooting us in the life of more people of our country.”

It’s understood that many in Labour who sympathize with Tony Blair’s New Labour vision, want the party to part ways with unions altogether. However, speaking on Sky News, the former prime minister said,  "I think this is a defining moment. It's bold and it's strong. It's real leadership, this. I think it's important not only in its own terms, because he's carrying through a process of reform in the Labour Party that is long overdue and, frankly, probably I should have done it when I was leader.”

Milliband is expected to be broadsided by both the Conservative Party, which will say his move reflects weakness, and by the unions, which will see this move as a way to dilute their power at Labour Party conferences.

The reforms will extend the idea of having primaries in choosing candidates for parliamentary seats when an MP retires outside of the general election period. Milliband is also set to announce a new code of conduct for those seeking to become parliamentary candidates and impose strict spending limits for selection campaigns.