Yup! It's a wildcat work action and it will be detected  

https://scholar.smu.edu/cgi/viewcontent.cgi?article=1886&context=jalcp>

V. CONCLUSION A carrier need not sit idly by in frustration while its employees engage in work slowdowns or sickouts during collective bargaining negotiations. Such activity is illegal and enjoinable. As unions have become more sophisticated in conducting such actions, union responsibility has become more difficult to prove. Statistical analysis provides carriers with a tool to use in meeting this challenge of proof. The binomial method in particular has served courts well in civil rights and employment discrimination cases. This method can serve equally well to aid carriers in challenging unlawful self help on the part of unions that otherwise might cause disruptions of commerce, passenger inconvenience, and irreparable economic injury to carriers.