Several republicans had asked Ney to leave the race to no avail, but Boehner has the ability to issue threats to Ney, ones he could very easily make due on. From The Washington Post:
House Majority Leader John A. Boehner (R-Ohio) met with Ney last week to urge him to step aside, reminding him that with a son in college and a daughter nearing college age, he will need money, according to several congressional Republican aides. If he lost his House seat for the party, Boehner is said to have cautioned, Ney could not expect a lucrative career on K Street to pay those tuition bills, along with the hundreds of thousands of dollars in legal fees piling up.
Personally, I'm not sure how powerful the licence plate manufacturing lobby is, but I know they don't get up to the Hill too often, tending to prefer to work out of a hotel of sorts.