Is it legal for my life insurance company to do this with less than a month's warning?
Usually, a term life insurance policy is issued with guaranteed level premiums for a specific period of time. Then, after the term ends the rate may increase at renewal.
Upon renewal, the new rate is based on your age at time of renewal, but if the policy has the renewability option you are not required to take a physical to renew the policy and the renewal rate cannot be increased due to your health.
If, for instance, you had a 20 year term life insurance policy and renewed it when the 20 years ended, your new rate based on your age 20 years after purchase of the first policy may be quite a bit higher than the original rate.
So, yes the rate for renewal may increase by more than 50%.
You can have your life insurance agent or financial planner review the life insurance contract to make sure the insurance company gave you proper notice of the increase in your premiums for your term life insurance policy.
If the premiums increased by more than 50% during the term of your policy, without advance notice, there may be an issue to review with the insurer and your attorney.
Ask the insurance company why the premium was increased and to show you in writing where the life insurance policy says they can increase your premiums by this much.
Also, you may want to compare term life insurance rates among other insurers and consider finding a more affordable term life insurance policy.