London — Prime Minister Margaret Thatcher hopes her policy of placing militant trade unions under firm legal restraint will be vindicated in a vital test case in the newspaper industry.
The focus of the dispute is a company near Manchester that has been trying to cite Thatcher government laws passed in 1980 and 1982 to justify its use of nonunion labor.
Earlier this year the Messenger group of newspapers sacked six members of the print trade union, the National Graphical Association (NGA). This sparked massive picketing at the company's plant at Warrington.
Clashes between thousands of NGA picketers and hundreds of police took place as the chairman of the Messenger group, Eddie Shah, printed his papers under conditions of siege and trucked them to surrounding areas under police escort.
Mrs. Thatcher regards the eventual outcome of the dispute as a likely watershed in union attitudes to the new industrial laws.
At the root of the confrontation between the NGA and Mr. Shah is the future of the so-called closed shop - the practice by trade unions of insisting that employees at a place of work to join trade unions.
Mrs. Thatcher wants to shatter the closed shop. The NGA and many other unions believe it should be retained.
In the Messenger dispute there is another central issue: The new industrial laws forbid ''secondary picketing'' - demonstrations by trade unionists not directly involved in a local dispute.
At Warrington, the six dismissed NGA workers received support from picketers from many centers in Britain. At the height of the clashes some 500 NGA picketers from London turned up outside the Messenger plant. At one point at least 4,000 picketers were trying to keep trucks loaded with newspapers from leaving the printing works.
In a series of legal actions, Shah and the Messenger group sought injunctions against the NGA. Fines of (STR)50,000 ($75,000) were imposed on the union. These were later trebled.
Eventually a court ruled that all of the NGA's funds, amounting to some (STR) 10 million ($15 million), should be sequestered, pending payment of the fines and a union readiness to abandon picketing at Warrington.
Mrs. Thatcher has tried to keep the government out of attempts to mediate an end to industrial disputes. She has favored the use of an independent concilia-tion service to sort out differences between managements and trade unions.
The conciliation service managed to arrange suspension of picketing at Warrington for a week while Shah and leaders of the NGA tried to reach a compromise.
Mrs. Thatcher has made no secret of her determination that the new laws must be upheld. Many pickets who went to Warrington from other cities said they did not recognize the new laws.
The Messenger case puts Britain's Trades Union Congress in an awkward position. The council of the TUC is split between a majority favoring reluctant acceptance of the new laws and a vociferous minority advocating confrontation.
The TUC's position is made all the more difficult by its decision earlier this year to hold discussions with the Thatcher government on wage policy.
Mrs. Thatcher has said the trade unions generally must accept the new laws. The Labour opposition favors acceptance of the laws but says the government must help resolve disputes.
A leading opposition spokesman urged Mrs. Thatcher to return to the ''beer and sandwiches at 10 Downing Street'' technique of solving industrial disputes. She rejected the suggestion.