Republican presidential candidate Donald Trump once again took aim at rivals Ted Cruz and John Kasich Monday night for joining forces to try and stop him from winning the GOP nomination before the part's convention, while Cruz said he was looking beyond Tuesday's five Eastern primaries.

The Cruz and Kasich campaigns announced Sunday that the Ohio governor would shift his campaign resources to give Cruz a clear run in Indiana, which votes on May 3. In return, the Texas senator's campaign would allow Kasich a clear path in Oregon — which holds its primary on May 17 — and New Mexico, which votes on June 7.

Trump told Fox News' Sean Hannity the move by the two campaigns was "collusion." 

"In business you go to jail for that, but it's collusion where they're coming together because they are getting beaten badly," he said. 

Trump continued to label Kasich as "1-for-42," a reference to the Ohio governor only winning his home state primary of all the Republican contests.

"If I would have campaigned two more days in Ohio, I would have won, but Kasich is doing terribly," Trump told Hannity.

Ahead of Tuesday's primary in Pennsylvania, Trump said despite what he called "a rigged system", he had high hopes of capturing most of the Keystone State's 71 delegates. 

"Fortunately in Pennsylvania you have a great head of the Republican party, you have a great head of the party and I think it will be fair," he said. "We hope we're going to win, we're going to win very big."

Cruz told Hannity that he was looking past Tuesday's contests in and focusing his energies on primaries in Midwestern and Western states, beginning in Indiana next week.

"As [the race] shifts back west, there are a lot of states that I think are going to be very good [for us]," he said. "It shifts to Indiana, it shifts to Nebraska, it shift to North Dakota, Montana, and then the big enchilada, California. California is 172 delegates and I believe we are going to do very well in California." 

He added that he foresees a contested Republican National Convention in Cleveland in July.

"Where we are now, nobody is going to get to 1,237 [pledged delegates]. The only way to win the nomination is to earn the majority of delegates and nobody is going to do that," Cruz said. "I'm not going to do it, but neither is Donald Trump, which means we are headed into a contested convention.

"I'll have a ton of delegates, he'll have a ton of delegates, and it's going to be a battle to see who can earn a majority of delegates elected by the people. And I think in that battle we will have a tremendous advantage."

However, Trump told Hannity that he believes that "millions of people" won't be happy to see a contested convention. 

"These are unbelievably dedicated people, they want to make America great again, they're not going to be happy, Sean. It's going to be disastrous I think, I really do," the real estate mogul said. "How do you put somebody that owns millions of more votes — I mean I'm up already like two and a half million votes over Cruz and much more than that over Kasich — how do you take that and say 'Oh, gee, we're going to go to the second ballot because of 25 delegates'?"