No, it is not acceptable to use pirated software to do your job, in fact it could lose you your job.
In the UK, the use of pirated software would usually be considered gross misconduct and be grounds for summary dismissal, so as risks go, that's a pretty big one.
As others have mentioned, the reason companies treat this so seriously is because the consequences for the company can be grave.
In the UK, The Federation Against Software Theft (FAST) publicises the legal penalties and security risks for piracy and prosecutes both organisations and individuals on behalf of its members. They also promote the use of Software Asset Management to help companies avoid copyright infringement.
Even using software provided by your company, if you know it to be pirated, could result in pretty dire consequences - it's not impossible that you could be considered to be a conspirator and personally liable.
Under such circumstances, ethically you should report the infringement to FAST (in the UK) and any repercussions for this should be covered by whistleblower legislation.
The situation in the US, or in any of the countries around the world whose legal system is based on the UK/UK models, would be pretty much the same.
The specific laws, crimes and enforcement agencies would be different, but the essential principal and the ethics of the situation would be identical.