SQL Server 2008R2 - data file grows back after shrinking and available to shrink again

After shrinking of datafile there is around 180Gb of free space on hard drive (prior to operation shrink file dialog also shows that it is possible to free up around 180Gb of space). After 1-2 days the datafile grows back to its original size (before shrink operation) and it is possible to shrink it again (Shrink file dialog shows again that it is possible to free up around 180Gb of space). I strictly forced to maintain some free space on hard drive, so avoiding the shrink operation is not an option. Looking for advice what could cause this issue and possible solution.