Despite support for the original legislation introduced by Dan Flynn, chair of the pensions committee in the Texas House of Representatives, Rawlings apparently took issue with a last minute addition to the bill that would have taxpayers fund the pensions of "phantom employees" based on a target Dallas police force of 3 officers per 1,000 residents.  Per ABC:

The clause sets a baseline number of officers and firefighters. In the case of police, that's three officers per thousand. The clause would also automatically assume that a certain level of raises given.
 
"Basically you're paying on phantom employees, not real employees," Rawlings said. "We just can't enter into an agreement with that degree of commitment for the city. No business would do it this way. We cannot find another pension fund in American where someone pays into a fund based on future employees. It's just not done and it should not start here in the State of Texas."
 
"This is the most taxpayer unfriendly poison pill that I've seen in this bill," he said. "I'm not going to swallow this pill."
Frankly, not wanting to spend taxpayer dollars to fund the pensions of officers that don't even exist just seems selfish, Mike!