Depends on the local laws, as usual. In germany everyone has the right to work part time, only in exceptional situations where a specific person is needed in full time the company can deny that, for example management pilots.
How the part time is designed is open to the employee. Of course CLAs about part time working can restrict some of that openness and are therefore liked by the employers.
In my current company the pilots do not have a CLA, but we have an (old) part time working scheme that defines several different part time working schedules. One way is to get full months off, up to 6, not more than 2 in a row. For each part time month base pay and vacation days are reduced by 1/12th, no per diems nor guaranteed hours are paid for the part time month, but for working months everything is the same as for a full time employee, except for the lower base pay. Another possibility is to get pro rata part time every month. It lowers the days available for the company (working days) by 5 or 10 (75% and 50% part time). Base pay and included hours are reduced, overtime will be paid once the lowered yearly hour limit (675, 450) has been passed. Part time has to be requested every year and will be awarded based on seniority and available capacity. Usually additional capacity will be made available for part time months later during the year.
And of course every employee has the right to request individually designed part time based on the law, many do that especially if they do not get their requested part time months via the normal company scheme, but quite a few use it to get part time that is different from the usual company part time.