Gov. Charlie Baker has until midnight tonight to veto a bill sent to him by the Legislature that would mandate insurance coverage for antibiotic lyme disease treatment. 

In a letter to lawmakers, Baker wrote that antibiotic therapy isn't clinically recognized as an appropriate treatment and he's got several medical experts to back him up. The cost of the mandate also has Baker worried, so he thinks employers and insurers need more time to look at the impact.

"While I support comprehensive coverage and access to Lyme Disease treatment, long-term antibiotic therapy is not clinically recognized as an appropriate form of treatment. Further, requiring coverage of experimental drugs for off-label use sets a concerning precedent. Finally, given the cost implications of this requirement, the commonwealth, employers, and insurers need time to assess and prepare for the fiscal impact of this proposal," Baker wrote.

The governor argues only specialists like rheumatologists—not general practitioners—should provide long-term care for Lyme disease under insurance policies.

Framingham state Rep. David Linsky has been fighting for the coverage for years. Linsky says the cost would be negligible and antibiotics have been successful for a lot of patients.

"The decision whether or not to do long term antibiotic treatment should not be left to the Legislature nor the governor, that decision should be left entirely to a patient and his or her physician," Linsky said.

If it comes to it, Linsky is confident lawmakers will override Baker's veto when they're in formal session this weekend.