(CNN)Here's a look at lockouts and strikes in professional sports. A lockout is imposed by management or the owners. A strike is initiated by the employees or players.
There have been six NFL work stoppages.
July 3-July 15, 1968 - The NFL Players Association votes to strike, and the NFL owners counter by locking out the players during training camp. The two sides come to an agreement regarding pension benefits, resulting in the first NFL collective bargaining agreement.
July 1-September 18, 1995 - The 80-day lockout revolves around the players dissatisfaction with their union and salaries.
June 21, 1995 - Owners and the players' union agree to a six-year deal.
There have been four work stoppages in the NHL since 1992, as a result of one strike and three lockouts.
April 1992 - NHL players go on strike, resulting in the postponement of 30 games.
There have been eight work stoppages in Major League Baseball history, as a result of five strikes and three lockouts.
April 1-13, 1972 - Strike concerning player pensions and binding arbitration. Lasts 13 days, 86 games missed.