Former Republican presidential candidate Mitt Romney has recorded a robo-call supporting Sen. Ted Cruz.

Romney, who lives in Utah, said he will caucus for Cruz on Tuesday in an effort to stop the momentum of Donald Trump, but he has not formally endorsed the senator from Texas.

"I'm calling to ask you to join me in supporting Ted Cruz for president this Tuesday," Romney said. "This is the time for Republicans across the spectrum to unite behind Ted. He is the only Republican candidate who can defeat Donald Trump, and at this point, a vote for John Kasich is a vote for Donald Trump."

Romney said that Cruz has "spent his life defending the Constitution," will bring back jobs and be a strong commander in chief.

"I’ll be voting for Ted Cruz this Tuesday, and I encourage you to do the same thing," Romney said.