It is not a good idea. Unless there is some further reason for denying father his rights, you should let him have his court ordered parenting time. You appear to know his reason, work, so he must have communicated with you. His working is good for your children, he is probably paying you child support, do you really want to his doing everything he is supposed to against him?
If he cannot pick up the children on Fridays but still has custody on Saturdays and Sundays, then yes, he has a right to take the children since he informed you that due to his work he will have to give up a portion of his custodial time. If this is a problem for you (to have the children on Fridays), you may modify the custody order amicably or through the court, but it would be unreasonable for you to deny him visitations altogether. It is easily predictable that he would file a petition to modify the custody order (to exclude Fridays but week weekends) if he is denied all visitation.
When the partial custody schedule was set up, it should have been set up around work schedules so that each of you would spend time with the child(ren) and on the basis that it was in the child(ren)'s best interests to have time with each parent. His work schedule changed and so normally the court would want the two of you to adjust the schedule to what is again in the child(ren)'s best interests with each of you having time wtih the child(ren) when each of you are available. If there is a reason that this change in schedule on Friday is difficult for you or the child(ren), then that needs to be addressed, but unless something has changed that it no longer is in the child(ren)'s best interests to spend time with father, denying him Saturdays and Sundays would seem to put you in a bad light if he took this back to court and does not seem to be in the child(ren)'s best interests based upon the information that you have provided.
This answer is only for informational purposes, is general in nature and does not constitute legal advice. This Q&A forum does not in any way create an attorney/client relationship. If you have a legal concern that is important to you, I urge you to consult with an attorney as a failure to take prompt and appropriate action on any rights that you may have could be prejudicial to them.