MP for Lichfield, Michael Fabricant, will introduce a Private Member's Bill in the Commons to make it illegal for employers to read private messages.
Fabricant, who is chairman of the Commons information select committee, said employees were already protected from bosses reading letters and listening to phone calls and they should get the same protection for e-mails.
He said, "While I appreciate that employers need to be satisfied that their employees are working during the hours for which they are paid, it does not give them the right to snoop into the private e-mails of their employees.
"My change to the law would give the same protection to e-mails as already exists for conventional mail and telephone calls."
E-mails could still be monitored by the police and security services to counter crime and terrorism, provided that they first obtained a court warrant, he added.